BILLY JOE REYNOLDS, Petitioner v. UNITED STATES. U.S. Supreme Court. Case No. 10-6549. Argued October 3, 2011 — Decided January 23, 2012. On Writ of Certiorari to the U.S. Court of Appeals for the Third Circuit.

Syllabus

The federal Sex Offender Registration and Notification Act (Act) requires convicted sex offenders to provide state governments with, and to update, information, e.g., names and current addresses, for state and federal sex offender registries. It is a crime if a person who is “required to register under [the Act]” and who “travels in interstate . . . commerce” knowingly “fails to register or update a registration.” 18 U.S.C. §2250(a). The Act defines “sex offender” to include offenders who were convicted before the Act’s effective date, 42 U.S.C. §16911(1), and says that “the Attorney General shall have the authority to specify the applicability of the [registration] requirements” to pre-Act offenders, §16913(d). The Act, which seeks to make more uniform and effective a patchwork of pre-Act federal and 50 state registration systems, became law in July 2006. In February 2007, the Attorney General promulgated an Interim Rule specifying that the Act applies to all pre-Act offenders. He has since promulgated further rules, regulations, and specifications.

Petitioner Reynolds, a pre-Act offender, registered in Missouri in 2005 but moved to Pennsylvania in September 2007 without updating the Missouri registration or registering in Pennsylvania. He was indicted for failing to meet the Act’s registration requirements between September 16 and October 16, 2007. He moved to dismiss the indictment on the ground that the Act was not applicable to pre-Act offenders during that time, arguing that the Attorney General’s February 2007 Interim Rule was invalid because it violated the Constitution’s “nondelegation” doctrine and the Administrative Procedure Act’s notice and comment requirements. The District Court rejected on the merits of Reynolds’ legal attack on the Interim Rule, but the Third Circuit rejected his argument without reaching the merits, concluding that the Act’s registration requirements applied to pre-Act offenders even in the absence of a rule by the Attorney General. Thus, it found, the Interim Rule’s validity made no legal difference in the outcome.

Held: The Act does not require pre-Act offenders to register before the Attorney General validly specifies that the Act’s registration provisions apply to them. Pp. 6-13.

(a) This conclusion is supported by a natural reading of the Act’s text, which consists of four statements. Statement One says that “[a] sex offender shall register, and keep the registration current.” Statement Two says that, generally, the offender must initially register before completing his “sentence of imprisonment.” Statement Three says that the sex offender must update a registration within three business days of any change of “name, residence, employment, or student status.” Statement Four says that “[t]he Attorney General shall have the authority to specify the applicability of the requirements . . . to sex offenders convicted before the enactment of” the Act. §16913. Read naturally, the Fourth Statement modifies the First. It deals specifically with a subset (pre-Act offenders) of the First Statement’s broad general class (all sex offenders) and thus should control the Act’s application to that subset. See Gozlon-Peretz v. United States, 498 U.S. 395, 407. Also, by giving the Attorney General authority to specify the Act’s “applicability,” not its “nonapplicability,” the Fourth Statement is more naturally read to confer authority to apply the Act, not authority to make exceptions. This reading efficiently resolves what may have been Congress’ concern about the practical problems of applying the new registration requirements to a large number of pre-Act offenders, which could have been expensive and might not have proved feasible to do immediately. It might have thought that such concerns warranted different treatment for different categories of pre-Act offenders. And it could have concluded that it was efficient and desirable to ask the Justice Department, charged with responsibility for implementation, to examine pre-Act offender problems and to apply the new requirements accordingly. This reading also takes Congress to have filled potential lacunae (created by related Act provisions) in a manner consistent with basic criminal law principles. The Second Statement, e.g., requires a sex offender to register before completing his prison term, but says nothing about when a pre-Act offender who has left prison is to register. An Attorney General ruling could diminish such uncertainties, helping to eliminate the kind of vagueness and uncertainty that criminal law must seek to avoid. Pp. 6-9.

(b) The Government’s three principal contrary arguments — that the Court’s reading conflicts with the Act’s purpose of establishing a national registration system that includes pre-Act offenders; that the Court’s reading could lead to an absurdly long implementation delay; and that the Act should be read to apply the requirements immediately and on their own to all pre-Act offenders to avoid the possibility that the Attorney General, who has, but is not required to use, “the authority to specify” requirements, might take no action — are unpersuasive. Some lower courts have read the Attorney General’s authority to apply only to pre-Act sex offenders who are unable to comply with the statute’s “initial registration” requirements, but that is not what the Act says. Pp. 9-13.

(c) Because the Act’s registration requirements do not apply to pre-Act offenders until the Attorney General so specifies, the question whether the Attorney General’s Interim Rule is a valid specification matters in this case. P. 13.
380 Fed. Appx. 125, reversed and remanded.

BREYER, J., delivered the opinion of the Court, in which ROBERTS, C. J., and KENNEDY, THOMAS, ALITO, SOTOMAYOR, and KAGAN, JJ., joined. SCALIA, J., filed a dissenting opinion, in which GINSBURG, J., joined.

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JUSTICE BREYER delivered the opinion of the Court.

The federal Sex Offender Registration and Notification Act (Act), 120 Stat. 590, 42 U.S.C. §16901 et seq. (2006 ed. and Supp. III), requires those convicted of certain sex crimes to provide state governments with (and to update) information, such as names and current addresses, for inclusion on state and federal sex offender registries. §§16912(a), 16913-16914, 16919(a) (2006 ed.). The Act makes it a crime for a person who is “required to register” under the Act and who “travels in interstate or foreign commerce” knowingly to “fai[l] to register or update a registration . . . .” 18 U.S.C. §2250(a). The question before us concerns the date on which this federal registration requirement took effect with respect to sex offenders convicted before the Act became law.

The Act defines the term “sex offender” as including these pre-Act offenders. 42 U.S.C. §16911(1); see Carr v. United States, 560 U.S. ___, ___ (2010) [22 Fla. L. Weekly Fed. S385a] (slip op., at 7). It says that “[a] sex offender shall register.” §16913(a). And it further says that“[t]he Attorney General shall have the authority to specify the applicability of the [registration] requirements . . . to sex offenders convicted before the enactment of this chapter . . . .” §16913(d) (emphasis added). In our view, these provisions, read together, mean that the Act’s registration requirements do not apply to pre-Act offenders until the Attorney General specifies that they do apply. We reverse a Court of Appeals determination that, in effect, holds the contrary.

I

A
The new federal Act reflects Congress’ awareness that pre-Act registration law consisted of a patchwork of federal and 50 individual state registration systems. See 73 Fed. Reg. 38045 (2008). The Act seeks to make those systems more uniform and effective. It does so by repealing several earlier federal laws that also (but less effectively) sought uniformity; by setting forth comprehensive registration-system standards; by making federal funding contingent on States’ bringing their systems into compliance with those standards; by requiring both state and federal sex offenders to register with relevant jurisdictions (and to keep registration information current); and by creating federal criminal sanctions applicable to those who violate the Act’s registration requirements. 18 U.S.C. §2250(a) (criminal provision); 42 U.S.C. §§16911(10), 16913-16916 (2006 ed. and Supp. III) (registration requirements); §16925 (federal funding); §129, 120 Stat. 600 (repeal of earlier laws).

The Act’s criminal penalty applies to “[w]ho[m]ever . . . is required to register under [the Act].” 18 U.S.C. §2250(a). It says that such a person (a federal sex offender or a nonfederal sex offender who travels in interstate commerce) must not knowingly fail “to register or update a registration as required by [the Act].” Ibid. (emphasis added); see Appendix, infra, at 14.

The relevant registration requirements are set forth in an Act provision that states:

“Registry requirements for sex offenders

“(a) In general

“A sex offender [defined to include any offender who was convicted of a sex offense] shall register, and keep the registration current, in each jurisdiction where the offender resides, where the offender is an employee, and where the offender is a student. . . .

“(b) Initial registration

“The sex offender shall initially register [either] before completing a sentence of imprisonment with respect to the offense giving rise to the registration requirement; or [for those not sentenced to prison] not later than 3 business days after being sentenced . . . .

“(c) Keeping the registration current

“A sex offender shall [update his registration within] 3 business days after each change of name, residence, employment, or student status [by] appear[ing] in person in at least 1 jurisdiction involved . . . and inform[ing] that jurisdiction of all [relevant] changes . . . .

“(d) Initial registration of sex offenders unable to comply with subsection (b)

“The Attorney General shall have the authority to specify the applicability of the [registration] requirements . . . to sex offenders convicted before the enactment of this chapter or its implementation in a particular jurisdiction, and to prescribe rules for the registration of any such sex offenders and for other categories of sex offenders who are unable to comply with subsection (b).” 42 U.S.C. §16913 (emphasis added).
The new Act became law on July 27, 2006.

On February 28, 2007, the Attorney General promulgated an Interim Rule specifying that “[t]he requirements of [the Act] apply to all sex offenders, including sex offenders convicted of the offense for which registration is required prior to the enactment of that Act.” 72 Fed. Reg. 8897 (codified at 28 CFR §72.3). Subsequently, the Attorney General promulgated further rules, regulations, and specifications. See 73 Fed. Reg. 38030 (2008); 75 Fed. Reg. 81849 (2010); 76 Fed. Reg. 1630 (2011). The present case focuses upon the applicability of the Act’s registration requirements to pre-Act offenders during the period between (1) July 27, 2006 (when the Act took effect) and (2) the moment when the Attorney General promulgated a valid rule specifying the registration requirements’ applicability, namely, February 28, 2007 (or a later date if the February 28 specification was invalid).

B
Billy Joe Reynolds, the petitioner, is a pre-Act offender. He was convicted of a Missouri sex offense in October 2001; he served four years in prison; he was released in July 2005; he then registered as a Missouri sex offender; but he moved to Pennsylvania in September 2007 without updating his Missouri registration information (as Missouri law required) and without registering in Pennsylvania. A federal grand jury indicted him, charging him with, between September 16 and October 16, 2007, having “knowingly failed to register and update a registration as required by [the Act].” App. 13; see 18 U.S.C. §2250(a). In the Government’s view, Reynolds’ failure to update his address information when he moved to Pennsylvania violated the requirement that a “sex offender” update registration information within “3 business days after each change of . . . residence.” 42 U.S.C. §16913(c).

Reynolds moved to dismiss the indictment on the ground that in September and October 2007 the Act’s registration requirements had not yet become applicable to pre-Act offenders. He conceded that the Act had become law earlier (namely, in July 2006), and he conceded that the Attorney General had already (in February 2007) promulgated an Interim Rule specifying that the Act’s registration requirements were applicable to pre-Act offenders. But he claimed that the Interim Rule was invalid because it violated both the Constitution’s “nondelegation” doctrine and the Administrative Procedure Act’s (APA) requirement for “good cause” to promulgate a rule without “notice and comment” (as the Attorney General had done). See A. L. A. Schechter Poultry Corp. v. United States, 295 U.S. 495, 529 (1935) (nondelegation doctrine); 5 U.S.C. §§553(b)(3)(B), (d)(3) (APA). Because the Interim Rule is invalid, he added, the law must treat him like a pre-Act offender who traveled interstate and violated the Act’s registration requirements before the Attorney General specified their applicability.

The District Court rejected on the merits Reynolds’ legal attack on the Interim Rule. But the Court of Appeals rejected Reynolds’ argument without reaching those merits. 380 Fed. Appx. 125 (2010). That court thought that the Act’s registration requirements apply to pre-Act offenders such as Reynolds (who was subject to a preexisting state-law registration requirement) from the date of the new law’s enactment — even in the absence of any rule or regulation by the Attorney General specifying that the new registration requirements apply. That being so, the validity of the Interim Rule could make no legal difference, for the Act required Reynolds to follow the new federal registration requirements regardless of any rulemaking.

The Courts of Appeals have reached different conclusions about whether the Act’s registration requirements apply to pre-Act offenders prior to the time that the Attorney General specifies their applicability, i.e., from July 2006 until at least February 2007. Six Circuits have held that the Act’s registration requirements do not apply to pre-Act offenders unless and until the Attorney General so specifies. United States v. Johnson, 632 F. 3d 912, 922-927 (CA5 2011); United States v. Valverde, 628 F. 3d 1159, 1162-1164 (CA9 2010); United States v. Cain, 583 F. 3d 408, 414-419 (CA6 2009); United States v. Hatcher, 560 F. 3d 222, 226-229 (CA4 2009); United States v. Dixon, 551 F. 3d 578, 585 (CA7 2008); United States v. Madera, 528 F. 3d 852, 856-859 (CA11 2008) (per curiam). Five Circuits have held that they apply from the date of the Act’s enactment, and prior to any such specification, at least with respect to pre-Act offenders who had already registered under state law. United States v. Fuller, 627 F. 3d 499, 506 (CA2 2010); United States v. DiTomasso, 621 F. 3d 17, 24 (CA1 2010); United States v. Shenandoah, 595 F. 3d 151, 163 (CA3 2010); United States v. Hinckley, 550 F. 3d 926, 932 (CA10 2008); United States v. May, 535 F. 3d 912, 918-919 (CA8 2008). In light of this split, we agreed to consider the question.

II

A
The question before us is whether the Act requires pre-Act offenders to register before the Attorney General validly specifies that the Act’s registration provisions apply to them. We believe that it does not. For one thing, a natural reading of the textual language supports our conclusion. The text consists of four statements. See supra, at 3. Statement One says that “[a] sex offender shall register, and keep the registration current.” Statement Two says that a sex offender must initially register before completing his “sentence of imprisonment” (or, if the sentence does not involve imprisonment, within three days of conviction). Statement Three says that the sex offender must update a registration within three business days of any change of “name, residence, employment, or student status.” Statement Four says that “[t]he Attorney General shall have the authority to specify the applicability of the requirements of this subchapter to sex offenders convicted before the enactment of this chapter.”

Read naturally, the Fourth Statement modifies the First. It specifically deals with a subset (pre-Act offenders) of a broad general class (all sex offenders) to which the First Statement applies. And it therefore should control the Act’s application to that subset. See Gozlon-Peretz v. United States, 498 U.S. 395, 407 (1991) (specific statutory provision normally controls over one of more general application); see also Bloate v. United States, 559 U.S. ___, ___ (2010) [22 Fla. L. Weekly Fed. S157b] (slip op., at 10) (same).

At the same time, the Fourth Statement says that the Attorney General has authority to specify the Act’s “applicability,” not its “nonapplicability.” And it consequently is more naturally read as conferring the authority to apply the Act, not the authority to make exceptions. That is how we normally understand a term such as “authority to specify” in the context of applying new rules to persons already governed by pre-existing rules. If, for example, the Major League Baseball Players Association and the team owners agreed that the Commissioner of Baseball “shall have the authority to specify the applicability” to the major leagues of the more stringent minor league drug testing policy, we should think that the minor league policy would not apply unless and until the Commissioner so specified.

For another thing, this reading of the Act efficiently resolves what Congress may well have thought were practical problems arising when the Act sought to apply the new registration requirements to pre-Act offenders. The problems arise out of the fact that the Act seeks to make more uniform a patchwork of pre-existing state systems. Doing so could require newly registering or re-registering “a large number” of pre-Act offenders. That effort could prove expensive. And it might not prove feasible to do so immediately. See 73 Fed. Reg. 38063 (recognizing these problems). Congress’ concern about these problems is reflected in the Act’s providing the States with three years to bring their systems into compliance with federal standards while permitting the Attorney General to extend that 3-year grace period to five years. 42 U.S.C. §16924.

These same considerations might have warranted different federal registration treatment of different categories of pre-Act offenders. Cf. 73 Fed. Reg. 38035-38036, and 38046-38047 (final Department of Justice guidelines allowing States to meet Act requirements without registering certain categories of pre-Act offenders); 76 Fed. Reg. 1635-1636 (supplemental guidelines allowing the same). At least Congress might well have so thought. And consequently, Congress might well have looked for a solution. Asking the Department of Justice, charged with responsibility for implementation, to examine these pre-Act offender problems and to apply the new registration requirements accordingly could have represented one efficient and desirable solution (though we express no view on Reynolds’ related constitutional claim). Cf. 42 U.S.C. §§16912(b), 16914(a)(7), (b)(7), 16919, 16941, 16945 (granting the Attorney General authority to administer various aspects of the Act). And that is just the solution that the Act’s language says that Congress adopted.

Finally, our reading of the Act takes Congress to have filled potential lacunae (created by related Act provisions) in a manner consistent with basic background principles of criminal law. The Second Statement, for example, says that a sex offender must register before completing his prison term, but the provision says nothing about when a pre-Act offender who completed his prison term pre-Act must register. Although a state pre-Act offender could not be prosecuted until he traveled interstate, there is no interstate requirement for a federal pre-Act offender. And to apply the Act to either of these pre-Act offenders from the date of enactment would require reading into the statute, silent on the point, some kind of unsaid equivalent (e.g., registering or updating within a “reasonable time” or “within three days of first post-Act travel in interstate commerce” or “as preexisting state law requires”).

Pre-Act offenders, aware of such complexities, lacunae, and difficulties, might, on their own, reach different conclusions about whether, or how, the new registration requirements applied to them. A ruling from the Attorney General, however, could diminish or eliminate those uncertainties, thereby helping to eliminate the very kind of vagueness and uncertainty that criminal law must seek to avoid. Cf., e.g., United States v. Lanier, 520 U.S. 259, 266 (1997) (noting that “the canon of strict construction of criminal statutes, or rule of lenity, ensures fair warning by so resolving ambiguity in a criminal statute as to apply it only to conduct clearly covered”).

B
The Government makes three principal arguments to the contrary. First, it says that our interpretation of the Act conflicts with one basic statutory purpose, namely, the “establish[ment of] a comprehensive national system for the registration of [sex] offenders,” 42 U.S.C. §16901, that includes offenders who committed their offenses before the Act became law. The Act reflects that purpose when it defines “sex offender” broadly to include any “individual who was convicted of a sex offense.” §16911(1). And we have recognized that purpose in stating that, in general, the Act’s criminal provisions apply to any pre-Act offender required to register under the Act who later travels interstate and fails to register. See Carr, 560 U.S., at ___ (slip op., at 7).

The Act’s history also reveals that many of its supporters placed considerable importance upon the registration of pre-Act offenders. See, e.g., H. R. Rep. No. 109-218, pt. 1, p. 24 (2005) (H. R. Rep.) (“[Twenty] percent of sexual offenders are ‘lost,’ and there is a strong public interest in finding them and having them register with current information to mitigate the risks of additional crimes against children”); 152 Cong. Rec. 15333 (2006) (statement of Sen. Cantwell) (“Child sex offenders have exploited this stunning lack of uniformity, and the consequences have been tragic. Twenty percent of the Nation’s 560,000 sex offenders are ‘lost’ because State offender registry programs are not coordinated well enough”); id., at 15338 (statement of Sen. Kyl) (“There currently are over 100,000 sex offenders in this country who are required to register but are ‘off the system.’ They are not registered. The penalties in this bill should be adequate to ensure that these individuals register”); id., at 13050 (statement of Sen. Frist) (“There are currently 550,000 registered sex offenders in the U.S. and at least 100,000 of them are missing from the system. Every day that we don’t have this national sex offender registry, these missing sex predators are out there somewhere”).

The difficulty with the Government’s argument, however, is that it overstates the need for instantaneous registration of pre-Act offenders. Our different reading, we concede, involves implementation delay. But that delay need not be long (the Attorney General issued his Interim Rule 217 days after the effective date of the new law). And that delay can be justified by the need to accommodate other Act-related interests. See supra, at 7-9.

Second, the Government suggests that our reading leads to an absurd result. As it points out, the Fourth Statement grants the Attorney General the “authority to specify” the registration requirements’ applicability not only to pre-Act offenders but also to those convicted prior to the “implementation” of the new Act “in a particular jurisdiction.” Some jurisdictions might not implement the Act for up to five years. See 42 U.S.C. § 16924; see also Dept. of Justice, Office of Justice Programs, Justice Department Finds 24 Jurisdictions Have Substantially Implemented SORNA Requirements (July 28, 2011) (stating that as of July 28, 2011, 14 States had implemented the Act’s requirements), http://www.ojp.usdoj.gov/newsroom/pressreleases/2011/SMART_PR-072811.htm (all Internet materials as visited Jan. 19, 2012, and available in Clerk of Court’s case file). Yet, the Government concludes, it is absurd to believe that Congress would have desired so long a delay in the application of its new registration requirements.

The problem with this argument, however, is that reading the two categories similarly (a matter which we need not decide) would not require a long delay in applying the registration requirements to post-Act offenders who committed a crime in a jurisdiction that is slow to implement the new requirements. At most, that reading would require the Attorney General to promulgate a rule applicable to all preimplementation offenders. That rule could specify that the Act’s preregistration provisions apply to some or to all those offenders. And it could do so quickly, well before a jurisdiction implements the Act’s requirements. Indeed, the Attorney General’s Interim Rule and the Department of Justice’s final guidelines, both issued before any jurisdiction implemented the Act’s requirements, state that the Act’s requirements apply to “all sex offenders,” including all preimplementation offenders. See 72 Fed. Reg. 8897 (codified at 28 CFR §72.3); 73 Fed. Reg. 38036; cf. Dept. of Justice, Office of Justice Programs, Justice Department Announces First Two Jurisdictions to Implement Sex Offender Registration and Notification Act (Sept. 23, 2009), http://www.ojp.usdoj.gov/newsroom/pressreleases/2009/SMART09154.htm.

Third, the Government argues against our interpretation on the ground that the Act says only that the Attorney General “shall have the authority to specify the applicability” of the Act’s registration requirements to pre-Act offenders; it does not say that he“shall specify” or otherwise require him to do so. The Act’s language, the Government continues, consequently gives the Attorney General the power not to specify anything; that power is inconsistent with Congress’ intent to ensure the speedy registration of thousands of “lost” pre-Act offenders, supra, at 10; and we can avoid this result only by reading the Act’s registration requirements as applying immediately and on their own to all pre-Act offenders (though the Attorney General would have the power to make exceptions).

This argument bases too much upon too little. There is no reason to believe that Congress feared that the Attorney General would refuse to apply the new requirements to pre-Act offenders. See, e.g., H. R. Rep., at 23-24; Protecting Our Nation’s Children from Sexual Predators and Violent Criminals: What Needs To Be Done? Hearing before the Subcommittee on Crime, Terrorism, and Homeland Security of the House Committee on the Judiciary, 109th Cong., 1st Sess., 4-13 (2005); Office of the Press Sec’y, The White House, President Signs H. R. 4472, the Adam Walsh Child Protection and Safety Act of 2006 (July 27, 2006), http://georgewbush-whitehouse.archives.gov/news/releases/2006/07/20060727-6.html. And there was no need for a mandatory requirement to avoid that unrealistic possibility. There is consequently no need to read the language unnaturally as giving the Attorney General the authority only to make exceptions from an implicit (unstated) rule that would otherwise apply the new registration requirements to all pre-Act offenders across the board and immediately.

Finally, we note that some lower courts have read the Attorney General’s specification authority as applying only to those pre-Act sex offenders unable to comply with the statute’s “initial registration” requirements. See 42 U.S.C. §16913(b). That, however, is not what the statute says. Rather, its Fourth Statement, §16913(d), says that the Attorney General has the authority (1) to specify the applicability of the registration requirements to pre-Act (and preimplementation) offenders, “and” (2) to prescribe rules for their registration, “and”(3) to prescribe registration rules for other categories of sex offenders who are unable to comply with the initial registration requirements. See supra, at 3. The word “and” means that the Attorney General’s authority extends beyond those pre-Act “sex offenders who are unable to comply” with the initial registration requirements.

III
For these reasons, we conclude that the Act’s registration requirements do not apply to pre-Act offenders until the Attorney General so specifies. Whether the Attorney General’s Interim Rule sets forth a valid specification consequently matters in the case before us. And we reverse the Third Circuit’s judgment to the contrary. We remand the case for further proceedings consistent with this opinion.

So ordered.

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APPENDIX
18 U.S.C. §2250(a)

“IN GENERAL. — Whoever —

“(1) is required to register under the Sex Offender Registration and Notification Act;

“(2)(A) is a sex offender as defined for the purposes of the Sex Offender Registration and Notification Act by reason of a conviction under Federal law (including the Uniform Code of Military Justice), the law of the District of Columbia, Indian tribal law, or the law of any territory or possession of the United States; or

“(B) travels in interstate or foreign commerce, or enters or leaves, or resides in, Indian country; and

“(3) knowingly fails to register or update a registration as required by the Sex Offender Registration and Notification Act;

“shall be fined under this title or imprisoned not more than 10 years, or both.”
42 U.S.C. §16913

“Registry requirements for sex offenders

“(a) In general

“A sex offender shall register, and keep the registration current, in each jurisdiction where the offender resides, where the offender is an employee, and where the offender is a student. For initial registration purposes only, a sex offender shall also register in the jurisdiction in which convicted if such jurisdiction is different from the jurisdiction of residence.

“(b) Initial registration

“The sex offender shall initially register — (1) before completing a sentence of imprisonment with respect to the offense giving rise to the registration requirement; or (2) not later than 3 business days after being sentenced for that offense, if the sex offender is not sentenced to a term of imprisonment.

“(c) Keeping the registration current

“A sex offender shall, not later than 3 business days after each change of name, residence, employment, or student status, appear in person in at least 1 jurisdiction involved pursuant to subsection (a) and inform that jurisdiction of all changes in the information required for that offender in the sex offender registry. That jurisdiction shall immediately provide that information to all other jurisdictions in which the offender is required to register.

“(d) Initial registration of sex offenders unable to comply with subsection (b)

“The Attorney General shall have the authority to specify the applicability of the requirements of this subchapter to sex offenders convicted before the enactment of this chapter or its implementation in a particular jurisdiction, and to prescribe rules for the registration of any such sex offenders and for other categories of sex offenders who are unable to comply with subsection (b).

“(e) State penalty for failure to comply

“Each jurisdiction, other than a Federally recognized Indian tribe, shall provide a criminal penalty that includes a maximum term of imprisonment that is greater than 1 year for the failure of a sex offender to comply with the requirements of this subchapter.”
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JUSTICE SCALIA, with whom JUSTICE GINSBURG joins, dissenting.

In my view, the registration requirements of the Sex Offender Registration and Notification Act (Act), 120 Stat. 590, 42 U.S.C. §16901 et seq. (2006 ed. and Supp. III), apply of their own force, without action by the Attorney General. The Act’s statement that “[t]he Attorney General shall have the authority to specify the applicability of the [registration] requirements” to pre-Act sex offenders, §16913(d), is best understood as conferring on the Attorney General an authority to make exceptions to the otherwise applicable registration requirements.

To begin with, I do not share the Court’s belief that to “specify the applicability” more naturally means, in the present context, to “make applicable” rather than to “make inapplicable.” See ante, at 7. The example the Court gives, the Commissioner of Baseball’s “ ‘authority to specify the applicability’ ” of more stringent minor-league drug testing policies to the major leagues, ibid., is entirely inapt, because it deals with a policy that on its face is otherwise not applicable. Since the major leagues are not covered by the policies, the Commissioner’s “ ‘authority to specify [their] applicability’ ” can mean nothing else but the authority to render them applicable. What we have here, however, is a statute that states in unqualified terms that “a sex offender shall register,” §16913(a) — and that the Court rightly believes was meant to cover pre-Act offenders.* The issue is whether “specify the applicability” means that no pre-Act offenders need register unless the Attorney General says so, or rather that the Attorney General may excuse the unqualified requirement for pre-Act offenders. In that context, it seems to me that the latter meaning is more natural. One specifies the applicability of an application that already exists by describing or revising its contours.

I think it preferable to give “specify” this meaning not only because here it is more natural, but also because the alternative is to read the statute as leaving it up to the Attorney General whether the registration requirement would ever apply to pre-Act offenders, even though registration of pre-Act offenders was (as the Court acknowledges) what the statute sought to achieve. For the statute does not instruct the Attorney General to specify; it merely gives him “authority” to do so. In this respect, the provision at issue here stands in marked contrast to other provisions of the Act which clearly impose duties on the Attorney General. See, e.g., §16912(b) (“The Attorney General shall issue guidelines and regulations to interpret and implement this subchapter”); §16917(b) (“The Attorney General shall prescribe rules for the notification of [certain] sex offenders”); §16919(a) (“The Attorney General shall maintain a national database”); §16926(a) (“The Attorney General shall establish and implement a Sex Offender Management Assistance program”).

The Court’s response to this — that “there was no need for a mandatory requirement to avoid [the] unrealistic possibility” that the Attorney General would not specify, ante, at 12-seems to me a fine answer to the question “What mandatory requirements must a poorly drafted statute contain in order to be workable?” It is an inadequate answer, however, to the question that is relevant here: “Would Congress have written the provision this way if it wanted pre-Act offenders covered and did not think they were covered absent specification by the Attorney General?” Intelligently drafted statutes make mandatory those executive acts essential to their functioning, whether or not those acts would likely occur anyway. It would have taken little effort (in fact, less effort) for Congress to write “the Attorney General shall specify the applicability” instead of “the Attorney General shall have authority to specify the applicability.” The latter formulation confers discretion, and it is simply implausible that the Attorney General was given discretion to determine whether coverage of pre-Act offenders (one of the purposes of the Act) should exist.

Indeed, it is not entirely clear to me that Congress can constitutionally leave it to the Attorney General to decide — with no statutory standard whatever governing his discretion — whether a criminal statute will or will not apply to certain individuals. That seems to me sailing close to the wind with regard to the principle that legislative powers are nondelegable, see Whitman v. American Trucking Assns., Inc., 531 U.S. 457, 472-476 (2001); Loving v. United States, 517 U.S. 748, 776-777 (1996) (SCALIA, J., concurring in part and concurring in judgment), and “[i]t is our settled policy to avoid an interpretation of a federal statute that engenders constitutional issues if a reasonable alternative interpretation poses no constitutional question.” Gomez v. United States, 490 U.S. 858, 864 (1989). Construing the Act to give the Attorney General the power to reduce congressionally imposed requirements fits that bill, because such a power is little more than a formalized version of the time-honored practice of prosecutorial discretion.

The Court points out that there might have been need for “different federal registration treatment of different categories of pre-Act offenders,” ante, at 8, and that absent a “ruling from the Attorney General” pre-Act offenders would be uncertain “about whether, or how, the new registration requirements applied to them,” ante, at 9. But attending to those details would certainly come within the Attorney General’s authority to “specify” application of the Act — and so would the temporary suspension of registration requirements pending the Attorney General’s resolution of those details. And of course the uncertainty of where to register could form the basis for the Attorney General’s exercise of his discretion not to prosecute in individual cases. Neither problem, it seems to me, justifies the extraordinary interpretation that this Act does not apply to pre-Act offenders unless and until the Attorney General, in his discretion, says so.

For these reasons, I respectfully dissent.

__________________

*The Court reaches this conclusion based on an inquiry into legislative history. See ante, at 9-10. That inquiry is quite superfluous, however since the text of the Act itself makes clear that Congress sought to “establis[h] a comprehensive national system for the registration of [sex offenders],” 42 U.S.C. §16901, with “sex offender” defined broadly to “mea[n] an individual who was convicted of a sex offense,” §16911(1) (emphasis added).

* * *

UNITED STATES, Petitioner v. ANTOINE JONES. U.S. Supreme Court. Case No. 10-1259. Argued November 8, 2011 — Decided January 23, 2012. On Writ of Certiorari to the U.S. Court of Appeals for the District of Columbia Circuit.

Syllabus

The Government obtained a search warrant permitting it to install a Global-Positioning-System (GPS) tracking device on a vehicle registered to respondent Jones’s wife. The warrant authorized installation in the District of Columbia and within 10 days, but agents installed the device on the 11th day and in Maryland. The Government then tracked the vehicle’s movements for 28 days. It subsequently secured an indictment of Jones and others on drug trafficking conspiracy charges. The District Court suppressed the GPS data obtained while the vehicle was parked at Jones’s residence, but held the remaining data admissible because Jones had no reasonable expectation of privacy when the vehicle was on public streets. Jones was convicted. The D. C. Circuit reversed, concluding that admission of the evidence obtained by warrantless use of the GPS device violated the Fourth Amendment.

Held: The Government’s attachment of the GPS device to the vehicle, and its use of that device to monitor the vehicle’s movements, constitutes a search under the Fourth Amendment. Pp. 3-12.

(a) The Fourth Amendment protects the “right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures.” Here, the Government’s physical intrusion on an “effect” for the purpose of obtaining information constitutes a “search.” This type of encroachment on an area enumerated in the Amendment would have been considered a search within the meaning of the Amendment at the time it was adopted. Pp. 3-4.

(b) This conclusion is consistent with this Court’s Fourth Amendment jurisprudence, which until the latter half of the 20th century was tied to common-law trespass. Later cases, which have deviated from that exclusively property-based approach, have applied the analysis of Justice Harlan’s concurrence in Katz v. United States, 389 U.S. 347, which said that the Fourth Amendment protects a person’s “reasonable expectation of privacy,” id., at 360. Here, the Court need not address the Government’s contention that Jones had no “reasonable expectation of privacy,” because Jones’s Fourth Amendment rights do not rise or fall with the Katz formulation. At bottom, the Court must “assur[e] preservation of that degree of privacy against government that existed when the Fourth Amendment was adopted.” Kyllo v. United States, 533 U.S. 27, 34. Katz did not repudiate the understanding that the Fourth Amendment embodies a particular concern for government trespass upon the areas it enumerates. The Katz reasonable-expectation-of-privacy test has been added to, but not substituted for, the common-law trespassory test. See Alderman v. United States, 394 U.S. 165, 176; Soldal v. Cook County, 506 U.S. 56, 64. United States v. Knotts, 460 U.S. 276, and United States v. Karo, 468 U.S. 705-post-Katz cases rejecting Fourth Amendment challenges to “beepers,” electronic tracking devices representing another form of electronic monitoring — do not foreclose the conclusion that a search occurred here. New York v. Class, 475 U.S. 106, and Oliver v. United States, 466 U.S. 170, also do not support the Government’s position. Pp. 4-12.

(c) The Government’s alternative argument — that if the attachment and use of the device was a search, it was a reasonable one — is forfeited because it was not raised below. P. 12.
615 F. 3d 544, affirmed.

SCALIA, J., delivered the opinion of the Court, in which ROBERTS, C. J., and KENNEDY, THOMAS, and SOTOMAYOR, JJ., joined. SOTOMAYOR, J., filed a concurring opinion. ALITO, J., filed an opinion concurring in the judgment, in which GINSBURG, BREYER, and KAGAN, JJ., joined.

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JUSTICE SCALIA delivered the opinion of the Court.

We decide whether the attachment of a Global-Positioning-System (GPS) tracking device to an individual’s vehicle, and subsequent use of that device to monitor the vehicle’s movements on public streets, constitutes a search or seizure within the meaning of the Fourth Amendment.

I
In 2004 respondent Antoine Jones, owner and operator of a nightclub in the District of Columbia, came under suspicion of trafficking in narcotics and was made the target of an investigation by a joint FBI and Metropolitan Police Department task force. Officers employed various investigative techniques, including visual surveillance of the nightclub, installation of a camera focused on the front door of the club, and a pen register and wiretap covering Jones’s cellular phone.

Based in part on information gathered from these sources, in 2005 the Government applied to the United States District Court for the District of Columbia for a warrant authorizing the use of an electronic tracking device on the Jeep Grand Cherokee registered to Jones’s wife. A warrant issued, authorizing installation of the device in the District of Columbia and within 10 days.

On the 11th day, and not in the District of Columbia but in Maryland,1 agents installed a GPS tracking device on the undercarriage of the Jeep while it was parked in a public parking lot. Over the next 28 days, the Government used the device to track the vehicle’s movements, and once had to replace the device’s battery when the vehicle was parked in a different public lot in Maryland. By means of signals from multiple satellites, the device established the vehicle’s location within 50 to 100 feet, and communicated that location by cellular phone to a Government computer. It relayed more than 2,000 pages of data over the 4-week period.

The Government ultimately obtained a multiple-count indictment charging Jones and several alleged coconspirators with, as relevant here, conspiracy to distribute and possess with intent to distribute five kilograms or more of cocaine and 50 grams or more of cocaine base, in violation of 21 U.S.C. §§841 and 846. Before trial, Jones filed a motion to suppress evidence obtained through the GPS device. The District Court granted the motion only in part, suppressing the data obtained while the vehicle was parked in the garage adjoining Jones’s residence. 451 F. Supp. 2d 71, 88 (2006). It held the remaining data admissible, because “ ‘[a] person traveling in an automobile on public thoroughfares has no reasonable expectation of privacy in his movements from one place to another.’ ” Ibid. (quoting United States v. Knotts, 460 U.S. 276, 281 (1983)). Jones’s trial in October 2006 produced a hung jury on the conspiracy count.

In March 2007, a grand jury returned another indictment, charging Jones and others with the same conspiracy. The Government introduced at trial the same GPS-derived locational data admitted in the first trial, which connected Jones to the alleged conspirators’ stash house that contained $850,000 in cash, 97 kilograms of cocaine, and 1 kilogram of cocaine base. The jury returned a guilty verdict, and the District Court sentenced Jones to life imprisonment.

The United States Court of Appeals for the District of Columbia Circuit reversed the conviction because of admission of the evidence obtained by warrantless use of the GPS device which, it said, violated the Fourth Amendment. United States v. Maynard, 615 F. 3d 544 (2010). The D. C. Circuit denied the Government’s petition for rehearing en banc, with four judges dissenting. 625 F. 3d 766 (2010). We granted certiorari, 564 U.S. ___ (2011).

II

A
The Fourth Amendment provides in relevant part that “[t]he right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated.” It is beyond dispute that a vehicle is an “effect” as that term is used in the Amendment. United States v. Chadwick, 433 U.S. 1, 12 (1977). We hold that the Government’s installation of a GPS device on a target’s vehicle,2 and its use of that device to monitor the vehicle’s movements, constitutes a “search.”

It is important to be clear about what occurred in this case: The Government physically occupied private property for the purpose of obtaining information. We have no doubt that such a physical intrusion would have been considered a “search” within the meaning of the Fourth Amendment when it was adopted. Entick v. Carrington, 95 Eng. Rep. 807 (C. P. 1765), is a “case we have described as a ‘monument of English freedom’ ‘undoubtedly familiar’ to ‘every American statesman’ at the time the Constitution was adopted, and considered to be ‘the true and ultimate expression of constitutional law’ ” with regard to search and seizure. Brower v. County of Inyo, 489 U.S. 593, 596 (1989) (quoting Boyd v. United States, 116 U.S. 616, 626 (1886)). In that case, Lord Camden expressed in plain terms the significance of property rights in search-and-seizure analysis:

“[O]ur law holds the property of every man so sacred, that no man can set his foot upon his neighbour’s close without his leave; if he does he is a trespasser, though he does no damage at all; if he will tread upon his neighbour’s ground, he must justify it by law.” Entick, supra, at 817.
The text of the Fourth Amendment reflects its close connection to property, since otherwise it would have referred simply to “the right of the people to be secure against unreasonable searches and seizures”; the phrase “in their persons, houses, papers, and effects” would have been superfluous.

Consistent with this understanding, our Fourth Amendment jurisprudence was tied to common-law trespass, at least until the latter half of the 20th century. Kyllo v. United States, 533 U.S. 27, 31 (2001) [14 Fla. L. Weekly Fed. S329a]; Kerr, The Fourth Amendment and New Technologies: Constitutional Myths and the Case for Caution, 102 Mich. L. Rev. 801, 816 (2004). Thus, in Olmstead v. United States, 277 U.S. 438 (1928), we held that wiretaps attached to telephone wires on the public streets did not constitute a Fourth Amendment search because “[t]here was no entry of the houses or offices of the defendants,” id., at 464.

Our later cases, of course, have deviated from that exclusively property-based approach. In Katz v. United States, 389 U.S. 347, 351 (1967), we said that “the Fourth Amendment protects people, not places,” and found a violation in attachment of an eavesdropping device to a public telephone booth. Our later cases have applied the analysis of Justice Harlan’s concurrence in that case, which said that a violation occurs when government officers violate a person’s “reasonable expectation of privacy,” id., at 360. See, e.g., Bond v. United States, 529 U.S. 334 (2000); California v. Ciraolo, 476 U.S. 207 (1986); Smith v. Maryland, 442 U.S. 735 (1979).

The Government contends that the Harlan standard shows that no search occurred here, since Jones had no “reasonable expectation of privacy” in the area of the Jeep accessed by Government agents (its underbody) and in the locations of the Jeep on the public roads, which were visible to all. But we need not address the Government’s contentions, because Jones’s Fourth Amendment rights do not rise or fall with the Katz formulation. At bottom, we must “assur[e] preservation of that degree of privacy against government that existed when the Fourth Amendment was adopted.” Kyllo, supra, at 34. As explained, for most of our history the Fourth Amendment was understood to embody a particular concern for government trespass upon the areas (“persons, houses, papers, and effects”) it enumerates.3 Katz did not repudiate that understanding. Less than two years later the Court upheld defendants’ contention that the Government could not introduce against them conversations between other people obtained by warrantless placement of electronic surveillance devices in their homes. The opinion rejected the dissent’s contention that there was no Fourth Amendment violation “unless the conversational privacy of the homeowner himself is invaded.”4 Alderman v. United States, 394 U.S. 165, 176 (1969). “[W]e [do not] believe that Katz, by holding that the Fourth Amendment protects persons and their private conversations, was intended to withdraw any of the protection which the Amendment extends to the home . . . .” Id., at 180.

More recently, in Soldal v. Cook County, 506 U.S. 56 (1992), the Court unanimously rejected the argument that although a “seizure” had occurred “in a ‘technical’ sense” when a trailer home was forcibly removed, id., at 62, no Fourth Amendment violation occurred because law enforcement had not “invade[d] the [individuals'] privacy,” id., at 60. Katz, the Court explained, established that “property rights are not the sole measure of Fourth Amendment violations,” but did not “snuf[f] out the previously recognized protection for property.” 506 U.S., at 64. As Justice Brennan explained in his concurrence in Knotts, Katz did not erode the principle “that, when the Government does engage in physical intrusion of a constitutionally protected area in order to obtain information, that intrusion may constitute a violation of the Fourth Amendment.” 460 U.S., at 286 (opinion concurring in judgment). We have embodied that preservation of past rights in our very definition of “reasonable expectation of privacy” which we have said to be an expectation “that has a source outside of the Fourth Amendment, either by reference to concepts of real or personal property law or to understandings that are recognized and permitted by society.” Minnesota v. Carter, 525 U.S. 83, 88 (1998) (internal quotation marks omitted). Katz did not narrow the Fourth Amendment’s scope.5

The Government contends that several of our post-Katz cases foreclose the conclusion that what occurred here constituted a search. It relies principally on two cases in which we rejected Fourth Amendment challenges to “beepers,” electronic tracking devices that represent another form of electronic monitoring. The first case, Knotts, upheld against Fourth Amendment challenge the use of a “beeper” that had been placed in a container of chloroform, allowing law enforcement to monitor the location of the container. 460 U.S., at 278. We said that there had been no infringement of Knotts’ reasonable expectation of privacy since the information obtained — the location of the automobile carrying the container on public roads, and the location of the off-loaded container in open fields near Knotts’ cabin — had been voluntarily conveyed to the public.6 Id., at 281-282. But as we have discussed, the Katz reasonable-expectation-of-privacy test has been added to, not substituted for, the common-law trespassory test. The holding in Knotts addressed only the former, since the latter was not at issue. The beeper had been placed in the container before it came into Knotts’ possession, with the consent of the then-owner. 460 U.S., at 278. Knotts did not challenge that installation, and we specifically declined to consider its effect on the Fourth Amendment analysis. Id., at 279, n. Knotts would be relevant, perhaps, if the Government were making the argument that what would otherwise be an unconstitutional search is not such where it produces only public information. The Government does not make that argument, and we know of no case that would support it.

The second “beeper” case, United States v. Karo, 468 U.S. 705 (1984), does not suggest a different conclusion. There we addressed the question left open by Knotts, whether the installation of a beeper in a container amounted to a search or seizure. 468 U.S., at 713. As in Knotts, at the time the beeper was installed the container belonged to a third party, and it did not come into possession of the defendant until later. 468 U.S., at 708. Thus, the specific question we considered was whether the installation “with the consent of the original owner constitute[d] a search or seizure . . . when the container is delivered to a buyer having no knowledge of the presence of the beeper.” Id., at 707 (emphasis added). We held not. The Government, we said, came into physical contact with the container only before it belonged to the defendant Karo; and the transfer of the container with the unmonitored beeper inside did not convey any information and thus did not invade Karo’s privacy. See id., at 712. That conclusion is perfectly consistent with the one we reach here. Karo accepted the container as it came to him, beeper and all, and was therefore not entitled to object to the beeper’s presence, even though it was used to monitor the container’s location. Cf. On Lee v. United States, 343 U.S. 747, 751-752 (1952) (no search or seizure where an informant, who was wearing a concealed microphone, was invited into the defendant’s business). Jones, who possessed the Jeep at the time the Government trespassorily inserted the information-gathering device, is on much different footing.

The Government also points to our exposition in New York v. Class, 475 U.S. 106 (1986), that “[t]he exterior of a car . . . is thrust into the public eye, and thus to examine it does not constitute a ‘search.’ ” Id., at 114. That statement is of marginal relevance here since, as the Government acknowledges, “the officers in this case did more than conduct a visual inspection of respondent’s vehicle,” Brief for United States 41 (emphasis added). By attaching the device to the Jeep, officers encroached on a protected area. In Class itself we suggested that this would make a difference, for we concluded that an officer’s momentary reaching into the interior of a vehicle did constitute a search.7 475 U.S., at 114-115.

Finally, the Government’s position gains little support from our conclusion in Oliver v. United States, 466 U.S. 170 (1984), that officers’ information-gathering intrusion on an “open field” did not constitute a Fourth Amendment search even though it was a trespass at common law, id., at 183. Quite simply, an open field, unlike the curtilage of a home, see United States v. Dunn, 480 U.S. 294, 300 (1987), is not one of those protected areas enumerated in the Fourth Amendment. Oliver, supra, at 176-177. See also Hester v. United States, 265 U.S. 57, 59 (1924). The Government’s physical intrusion on such an area — unlike its intrusion on the “effect” at issue here — is of no Fourth Amendment significance.8

B
The concurrence begins by accusing us of applying “18th-century tort law.” Post, at 1. That is a distortion. What we apply is an 18th-century guarantee against unreasonable searches, which we believe must provide at a minimum the degree of protection it afforded when it was adopted. The concurrence does not share that belief. It would apply exclusively Katz’s reasonable-expectation-of-privacy test, even when that eliminates rights that previously existed.

The concurrence faults our approach for “present[ing] particularly vexing problems” in cases that do not involve physical contact, such as those that involve the transmission of electronic signals. Post, at 9. We entirely fail to understand that point. For unlike the concurrence, which would make Katz the exclusive test, we do not make trespass the exclusive test. Situations involving merely the transmission of electronic signals without trespass would remain subject to Katz analysis.

In fact, it is the concurrence’s insistence on the exclusivity of the Katz test that needlessly leads us into “particularly vexing problems” in the present case. This Court has to date not deviated from the understanding that mere visual observation does not constitute a search. See Kyllo, 533 U.S., at 31-32. We accordingly held in Knotts that “[a] person traveling in an automobile on public thoroughfares has no reasonable expectation of privacy in his movements from one place to another.” 460 U.S., at 281. Thus, even assuming that the concurrence is correct to say that “[t]raditional surveillance” of Jones for a 4-week period “would have required a large team of agents, multiple vehicles, and perhaps aerial assistance,” post, at 12, our cases suggest that such visual observation is constitutionally permissible. It may be that achieving the same result through electronic means, without an accompanying trespass, is an unconstitutional invasion of privacy, but the present case does not require us to answer that question.

And answering it affirmatively leads us needlessly into additional thorny problems. The concurrence posits that “relatively short-term monitoring of a person’s movements on public streets” is okay, but that “the use of longer term GPS monitoring in investigations of most offenses”is no good. Post, at 13 (emphasis added). That introduces yet another novelty into our jurisprudence. There is no precedent for the proposition that whether a search has occurred depends on the nature of the crime being investigated. And even accepting that novelty, it remains unexplained why a 4-week investigation is “surely” too long and why a drug-trafficking conspiracy involving substantial amounts of cash and narcotics is not an “extraordinary offens[e]” which may permit longer observation. See post, at 13-14. What of a 2-day monitoring of a suspected purveyor of stolen electronics? Or of a 6-month monitoring of a suspected terrorist? We may have to grapple with these “vexing problems” in some future case where a classic trespassory search is not involved and resort must be had to Katz analysis; but there is no reason for rushing forward to resolve them here.

III
The Government argues in the alternative that even if the attachment and use of the device was a search, it was reasonable — and thus lawful — under the Fourth Amendment because “officers had reasonable suspicion, and indeed probable cause, to believe that [Jones] was a leader in a large-scale cocaine distribution conspiracy.” Brief for United States 50-51. We have no occasion to consider this argument. The Government did not raise it below, and the D. C. Circuit therefore did not address it. See 625 F. 3d, at 767 (Ginsburg, Tatel, and Griffith, JJ., concurring in denial of rehearing en banc). We consider the argument forfeited. See Sprietsma v. Mercury Marine, 537 U.S. 51, 56, n. 4 (2002).

* * *
The judgment of the Court of Appeals for the D. C. Circuit is affirmed.

It is so ordered.

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1In this litigation, the Government has conceded noncompliance with the warrant and has argued only that a warrant was not required. United States v. Maynard, 615 F. 3d 544, 566, n. (CADC 2010).

2As we have noted, the Jeep was registered to Jones’s wife. The Government acknowledged, however, that Jones was “the exclusive driver.” Id., at 555, n. (internal quotation marks omitted). If Jones was not the owner he had at least the property rights of a bailee. The Court of Appeals concluded that the vehicle’s registration did not affect his ability to make a Fourth Amendment objection, ibid., and the Government has not challenged that determination here. We therefore do not consider the Fourth Amendment significance of Jones’s status.

3JUSTICE ALITO’s concurrence (hereinafter concurrence) doubts the wisdom of our approach because “it is almost impossible to think of late-18th-century situations that are analogous to what took place in this case.” Post, at 3 (opinion concurring in judgment). But in fact it posits a situation that is not far afield — a constable’s concealing himself in the target’s coach in order to track its movements. Ibid. There is no doubt that the information gained by that trespassory activity would be the product of an unlawful search — whether that information consisted of the conversations occurring in the coach, or of the destinations to which the coach traveled.

In any case, it is quite irrelevant whether there was an 18th-century analog. Whatever new methods of investigation may be devised, our task, at a minimum, is to decide whether the action in question would have constituted a “search” within the original meaning of the Fourth Amendment. Where, as here, the Government obtains information by physically intruding on a constitutionally protected area, such a search has undoubtedly occurred.

4Thus, the concurrence’s attempt to recast Alderman as meaning that individuals have a “legitimate expectation of privacy in all conversations that [take] place under their roof,” post, at 6-7, is foreclosed by the Court’s opinion. The Court took as a given that the homeowner’s “conversational privacy” had not been violated.

5The concurrence notes that post-Katz we have explained that “ ‘an actual trespass is neither necessary nor sufficient to establish a constitutional violation.’ ” Post, at 6 (quoting United States v. Karo, 468 U.S. 705, 713 (1984)). That is undoubtedly true, and undoubtedly irrelevant. Karo was considering whether a seizure occurred, and as the concurrence explains, a seizure of property occurs, not when there is a trespass, but “when there is some meaningful interference with an individual’s possessory interests in that property.” Post, at 2 (internal quotation marks omitted). Likewise with a search. Trespass alone does not qualify, but there must be conjoined with that what was present here: an attempt to find something or to obtain information.

Related to this, and similarly irrelevant, is the concurrence’s point that, if analyzed separately, neither the installation of the device nor its use would constitute a Fourth Amendment search. See ibid. Of course not. A trespass on “houses” or “effects,” or a Katz invasion of privacy, is not alone a search unless it is done to obtain information; and the obtaining of information is not alone a search unless it is achieved by such a trespass or invasion of privacy.

6Knotts noted the “limited use which the government made of the signals from this particular beeper,” 460 U.S., at 284; and reserved the question whether “different constitutional principles may be applicable” to “dragnet-type law enforcement practices” of the type that GPS tracking made possible here, ibid.

7The Government also points to Cardwell v. Lewis, 417 U.S. 583 (1974), in which the Court rejected the claim that the inspection of an impounded vehicle’s tire tread and the collection of paint scrapings from its exterior violated the Fourth Amendment. Whether the plurality said so because no search occurred or because the search was reasonable is unclear. Compare id., at 591 (opinion of Blackmun, J.) (“[W]e fail to comprehend what expectation of privacy was infringed”), with id., at 592 (“Under circumstances such as these, where probable cause exists, a warrantless examination of the exterior of a car is not unreasonable . . . ”).

8Thus, our theory is not that the Fourth Amendment is concerned with “any technical trespass that led to the gathering of evidence.” Post, at 3 (ALITO, J., concurring in judgment) (emphasis added). The Fourth Amendment protects against trespassory searches only with regard to those items (“persons, houses, papers, and effects”) that it enumerates. The trespass that occurred in Oliver may properly be understood as a “search,” but not one “in the constitutional sense.” 466 U.S., at 170, 183.

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JUSTICE SOTOMAYOR, concurring.

I join the Court’s opinion because I agree that a search within the meaning of the Fourth Amendment occurs, at a minimum, “[w]here, as here, the Government obtains information by physically intruding on a constitutionally protected area.” Ante, at 6, n. 3. In this case, the Government installed a Global Positioning System (GPS) tracking device on respondent Antoine Jones’ Jeep without a valid warrant and without Jones’ consent, then used that device to monitor the Jeep’s movements over the course of four weeks. The Government usurped Jones’ property for the purpose of conducting surveillance on him, thereby invading privacy interests long afforded, and undoubtedly entitled to, Fourth Amendment protection. See, e.g., Silverman v. United States, 365 U.S. 505, 511-512 (1961).

Of course, the Fourth Amendment is not concerned only with trespassory intrusions on property. See, e.g., Kyllo v. United States, 533 U.S. 27, 31-33 (2001). Rather, even in the absence of a trespass, “a Fourth Amendment search occurs when the government violates a subjective expectation of privacy that society recognizes as reasonable.” Id., at 33; see also Smith v. Maryland, 442 U.S. 735, 740-741 (1979); Katz v. United States, 389 U.S. 347, 361 (1967) (Harlan, J., concurring). In Katz, this Court enlarged its then-prevailing focus on property rights by announcing that the reach of the Fourth Amendment does not “turn upon the presence or absence of a physical intrusion.” Id., at 353. As the majority’s opinion makes clear, however, Katz’s reasonable-expectation-of-privacy test augmented, but did not displace or diminish, the common-law trespassory test that preceded it. Ante, at 8. Thus, “when the Government does engage in physical intrusion of a constitutionally protected area in order to obtain information, that intrusion may constitute a violation of the Fourth Amendment.” United States v. Knotts, 460 U.S. 276, 286 (1983) (Brennan, J., concurring in judgment); see also, e.g., Rakas v. Illinois, 439 U.S. 128, 144, n. 12 (1978). JUSTICE ALITO’s approach, which discounts altogether the constitutional relevance of the Government’s physical intrusion on Jones’ Jeep, erodes that longstanding protection for privacy expectations inherent in items of property that people possess or control. See post, at 5-7 (opinion concurring in judgment). By contrast, the trespassory test applied in the majority’s opinion reflects an irreducible constitutional minimum: When the Government physically invades personal property to gather information, a search occurs. The reaffirmation of that principle suffices to decide this case.

Nonetheless, as JUSTICE ALITO notes, physical intrusion is now unnecessary to many forms of surveillance. Post, at 9-12. With increasing regularity, the Government will be capable of duplicating the monitoring undertaken in this case by enlisting factory- or owner-installed vehicle tracking devices or GPS-enabled smartphones. See United States v. Pineda-Moreno, 617 F. 3d 1120, 1125 (CA9 2010) (Kozinski, C. J., dissenting from denial of rehearing en banc). In cases of electronic or other novel modes of surveillance that do not depend upon a physical invasion on property, the majority opinion’s trespassory test may provide little guidance. But “[s]ituations involving merely the transmission of electronic signals without trespass would remain subject to Katz analysis.” Ante, at 11. As JUSTICE ALITO incisively observes, the same technological advances that have made possible nontrespassory surveillance techniques will also affect the Katz test by shaping the evolution of societal privacy expectations. Post, at 10-11. Under that rubric, I agree with JUSTICE ALITO that, at the very least, “longer term GPS monitoring in investigations of most offenses impinges on expectations of privacy.” Post, at 13.

In cases involving even short-term monitoring, some unique attributes of GPS surveillance relevant to the Katz analysis will require particular attention. GPS monitoring generates a precise, comprehensive record of a person’s public movements that reflects a wealth of detail about her familial, political, professional, religious, and sexual associations. See, e.g., People v. Weaver, 12 N. Y. 3d 433, 441-442, 909 N. E. 2d 1195, 1199 (2009) (“Disclosed in [GPS] data . . . will be trips the indisputably private nature of which takes little imagination to conjure: trips to the psychiatrist, the plastic surgeon, the abortion clinic, the AIDS treatment center, the strip club, the criminal defense attorney, the by-the-hour motel, the union meeting, the mosque, synagogue or church, the gay bar and on and on”). The Government can store such records and efficiently mine them for information years into the future. Pineda-Moreno, 617 F. 3d, at 1124 (opinion of Kozinski, C. J.). And because GPS monitoring is cheap in comparison to conventional surveillance techniques and, by design, proceeds surreptitiously, it evades the ordinary checks that constrain abusive law enforcement practices: “limited police resources and community hostility.” Illinois v. Lidster, 540 U.S. 419, 426 (2004).

Awareness that the Government may be watching chills associational and expressive freedoms. And the Government’s unrestrained power to assemble data that reveal private aspects of identity is susceptible to abuse. The net result is that GPS monitoring — by making available at a relatively low cost such a substantial quantum of intimate information about any person whom the Government, in its unfettered discretion, chooses to track — may “alter the relationship between citizen and government in a way that is inimical to democratic society.” United States v. Cuevas-Perez, 640 F. 3d 272, 285 (CA7 2011) (Flaum, J., concurring).

I would take these attributes of GPS monitoring into account when considering the existence of a reasonable societal expectation of privacy in the sum of one’s public movements. I would ask whether people reasonably expect that their movements will be recorded and aggregated in a manner that enables the Government to ascertain, more or less at will, their political and religious beliefs, sexual habits, and so on. I do not regard as dispositive the fact that the Government might obtain the fruits of GPS monitoring through lawful conventional surveillance techniques. See Kyllo, 533 U.S., at 35, n. 2; ante, at 11 (leaving open the possibility that duplicating traditional surveillance “through electronic means, without an accompanying trespass, is an unconstitutional invasion of privacy”). I would also consider the appropriateness of entrusting to the Executive, in the absence of any oversight from a coordinate branch, a tool so amenable to misuse, especially in light of the Fourth Amendment’s goal to curb arbitrary exercises of police power to and prevent “a too permeating police surveillance,” United States v. Di Re, 332 U.S. 581, 595 (1948).*

More fundamentally, it may be necessary to reconsider the premise that an individual has no reasonable expectation of privacy in information voluntarily disclosed to third parties. E.g., Smith, 442 U.S., at 742; United States v. Miller, 425 U.S. 435, 443 (1976). This approach is ill suited to the digital age, in which people reveal a great deal of information about themselves to third parties in the course of carrying out mundane tasks. People disclose the phone numbers that they dial or text to their cellular providers; the URLs that they visit and the e-mail addresses with which they correspond to their Internet service providers; and the books, groceries, and medications they purchase to online retailers. Perhaps, as JUSTICE ALITO notes, some people may find the “tradeoff” of privacy for convenience “worthwhile,” or come to accept this “diminution of privacy” as “inevitable,” post, at 10, and perhaps not. I for one doubt that people would accept without complaint the warrantless disclosure to the Government of a list of every Web site they had visited in the last week, or month, or year. But whatever the societal expectations, they can attain constitutionally protected status only if our Fourth Amendment jurisprudence ceases to treat secrecy as a prerequisite for privacy. I would not assume that all information voluntarily disclosed to some member of the public for a limited purpose is, for that reason alone, disentitled to Fourth Amendment protection. See Smith, 442 U.S., at 749 (Marshall, J., dissenting) (“Privacy is not a discrete commodity, possessed absolutely or not at all. Those who disclose certain facts to a bank or phone company for a limited business purpose need not assume that this information will be released to other persons for other purposes”); see also Katz, 389 U.S., at 351-352 (“[W]hat [a person] seeks to preserve as private, even in an area accessible to the public, may be constitutionally protected”).

Resolution of these difficult questions in this case is unnecessary, however, because the Government’s physical intrusion on Jones’ Jeep supplies a narrower basis for decision. I therefore join the majority’s opinion.

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*United States v. Knotts, 460 U.S. 276 (1983), does not foreclose the conclusion that GPS monitoring, in the absence of a physical intrusion, is a Fourth Amendment search. As the majority’s opinion notes, Knotts reserved the question whether “ ‘different constitutional principles may be applicable’ ” to invasive law enforcement practices such as GPS tracking. See ante, at 8, n. 6 (quoting 460 U.S., at 284).

United States v. Karo, 468 U.S. 705 (1984), addressed the Fourth Amendment implications of the installation of a beeper in a container with the consent of the container’s original owner, who was aware that the beeper would be used for surveillance purposes. Id., at 707. Owners of GPS-equipped cars and smartphones do not contemplate that these devices will be used to enable covert surveillance of their movements. To the contrary, subscribers of one such service greeted a similar suggestion with anger. Quain, Changes to OnStar’s Privacy Terms Rile Some Users, N. Y. Times (Sept. 22, 2011), online at http://wheels.blogs.nytimes. com/2011/09/22/changes-to-onstars-privacy-terms-rile-some-users (as visited Jan. 19, 2012, and available in Clerk of Court’s case file). In addition, the bugged container in Karo lacked the close relationship with the target that a car shares with its owner. The bugged container in Karo was stationary for much of the Government’s surveillance. See 468 U.S., at 708-710. A car’s movements, by contrast, are its owner’s movements.

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JUSTICE ALITO, with whom JUSTICE GINSBURG, JUSTICE BREYER, and JUSTICE KAGAN join, concurring in the judgment.

This case requires us to apply the Fourth Amendment’s prohibition of unreasonable searches and seizures to a 21st-century surveillance technique, the use of a Global Positioning System (GPS) device to monitor a vehicle’s movements for an extended period of time. Ironically, the Court has chosen to decide this case based on 18th-century tort law. By attaching a small GPS device1 to the underside of the vehicle that respondent drove, the law enforcement officers in this case engaged in conduct that might have provided grounds in 1791 for a suit for trespass to chattels.2 And for this reason, the Court concludes, the installation and use of the GPS device constituted a search. Ante, at 3-4.

This holding, in my judgment, is unwise. It strains the language of the Fourth Amendment; it has little if any support in current Fourth Amendment case law; and it is highly artificial.

I would analyze the question presented in this case by asking whether respondent’s reasonable expectations of privacy were violated by the long-term monitoring of the movements of the vehicle he drove.

I

A
The Fourth Amendment prohibits “unreasonable searches and seizures,” and the Court makes very little effort to explain how the attachment or use of the GPS device fits within these terms. The Court does not contend that there was a seizure. A seizure of property occurs when there is “some meaningful interference with an individual’s possessory interests in that property,” United States v. Jacobsen, 466 U.S. 109, 113 (1984), and here there was none. Indeed, the success of the surveillance technique that the officers employed was dependent on the fact that the GPS did not interfere in any way with the operation of the vehicle, for if any such interference had been detected, the device might have been discovered.

The Court does claim that the installation and use of the GPS constituted a search, see ante, at 3-4, but this conclusion is dependent on the questionable proposition that these two procedures cannot be separated for purposes of Fourth Amendment analysis. If these two procedures are analyzed separately, it is not at all clear from the Court’s opinion why either should be regarded as a search. It is clear that the attachment of the GPS device was not itself a search; if the device had not functioned or if the officers had not used it, no information would have been obtained. And the Court does not contend that the use of the device constituted a search either. On the contrary, the Court accepts the holding in United States v. Knotts, 460 U.S. 276 (1983), that the use of a surreptitiously planted electronic device to monitor a vehicle’s movements on public roads did not amount to a search. See ante, at 7.

The Court argues — and I agree — that “we must ‘assur[e] preservation of that degree of privacy against government that existed when the Fourth Amendment was adopted.’ ” Ante, at 5 (quoting Kyllo v. United States, 533 U.S. 27, 34 (2001)). But it is almost impossible to think of late-18th-century situations that are analogous to what took place in this case. (Is it possible to imagine a case in which a constable secreted himself somewhere in a coach and remained there for a period of time in order to monitor the movements of the coach’s owner?3) The Court’s theory seems to be that the concept of a search, as originally understood, comprehended any technical trespass that led to the gathering of evidence, but we know that this is incorrect. At common law, any unauthorized intrusion on private property was actionable, see Prosser & Keeton 75, but a trespass on open fields, as opposed to the “curtilage” of a home, does not fall within the scope of the Fourth Amendment because private property outside the curtilage is not part of a “hous[e]” within the meaning of the Fourth Amendment. See Oliver v. United States, 466 U.S. 170 (1984); Hester v. United States, 265 U.S. 57 (1924).

B
The Court’s reasoning in this case is very similar to that in the Court’s early decisions involving wiretapping and electronic eavesdropping, namely, that a technical trespass followed by the gathering of evidence constitutes a search. In the early electronic surveillance cases, the Court concluded that a Fourth Amendment search occurred when private conversations were monitored as a result of an “unauthorized physical penetration into the premises occupied” by the defendant. Silverman v. United States, 365 U.S. 505, 509 (1961). In Silverman, police officers listened to conversations in an attached home by inserting a “spike mike” through the wall that this house shared with the vacant house next door. Id., at 506. This procedure was held to be a search because the mike made contact with a heating duct on the other side of the wall and thus “usurp [ed] . . . an integral part of the premises.” Id., at 511.

By contrast, in cases in which there was no trespass, it was held that there was no search. Thus, in Olmstead v. United States, 277 U.S. 438 (1928), the Court found that the Fourth Amendment did not apply because “[t]he taps from house lines were made in the streets near the houses.” Id., at 457. Similarly, the Court concluded that no search occurred in Goldman v. United States, 316 U.S. 129, 135 (1942), where a “detectaphone” was placed on the outer wall of defendant’s office for the purpose of overhearing conversations held within the room.

This trespass-based rule was repeatedly criticized. In Olmstead, Justice Brandeis wrote that it was “immaterial where the physical connection with the telephone wires was made.” 277 U.S., at 479 (dissenting opinion). Although a private conversation transmitted by wire did not fall within the literal words of the Fourth Amendment, he argued, the Amendment should be understood as prohibiting “every unjustifiable intrusion by the government upon the privacy of the individual.” Id., at 478. See also, e.g., Silverman, supra, at 513 (Douglas, J., concurring) (“The concept of ‘an unauthorized physical penetration into the premises,’ on which the present decision rests seems to me beside the point. Was not the wrong . . . done when the intimacies of the home were tapped, recorded, or revealed? The depth of the penetration of the electronic device — even the degree of its remoteness from the inside of the house — is not the measure of the injury”); Goldman, supra, at 139 (Murphy, J., dissenting) (“[T]he search of one’s home or office no longer requires physical entry, for science has brought forth far more effective devices for the invasion of a person’s privacy than the direct and obvious methods of oppression which were detested by our forebears and which inspired the Fourth Amendment”).

Katz v. United States, 389 U.S. 347 (1967), finally did away with the old approach, holding that a trespass was not required for a Fourth Amendment violation. Katz involved the use of a listening device that was attached to the outside of a public telephone booth and that allowed police officers to eavesdrop on one end of the target’s phone conversation. This procedure did not physically intrude on the area occupied by the target, but the Katz Court, “repudiate[ed]” the old doctrine, Rakas v. Illinois, 439 U.S. 128, 143 (1978), and held that “[t]he fact that the electronic device employed . . . did not happen to penetrate the wall of the booth can have no constitutional significance,” 389 U.S., at 353 (“[T]he reach of th[e] [Fourth] Amendment cannot turn upon the presence or absence of a physical intrusion into any given enclosure”); see Rakas, supra, at 143 (describing Katz as holding that the “capacity to claim the protection for the Fourth Amendment depends not upon a property right in the invaded place but upon whether the person who claims the protection of the Amendment has a legitimate expectation of privacy in the invaded place”); Kyllo, supra, at 32 (“We have since decoupled violation of a person’s Fourth Amendment rights from trespassory violation of his property”). What mattered, the Court now held, was whether the conduct at issue “violated the privacy upon which [the defendant] justifiably relied while using the telephone booth.” Katz, supra, at 353.

Under this approach, as the Court later put it when addressing the relevance of a technical trespass, “an actual trespass is neither necessary nor sufficient to establish a constitutional violation.” United States v. Karo, 468 U.S. 705, 713 (1984) (emphasis added). Ibid. (“Compar[ing] Katz v. United States, 389 U.S. 347 (1967) (no trespass, but Fourth Amendment violation), with Oliver v. United States, 466 U.S. 170 (1984) (trespass, but no Fourth Amendment violation)”). In Oliver, the Court wrote:

“The existence of a property right is but one element in determining whether expectations of privacy are legitimate. ‘The premise that property interests control the right of the Government to search and seize has been discredited.’ Katz, 389 U.S., at 353, (quoting Warden v. Hayden, 387 U.S. 294, 304 (1967); some internal quotation marks omitted).” 466 U.S., at 183.

II
The majority suggests that two post-Katz decisions — Soldal v. Cook County, 506 U.S. 56 (1992), and Alderman v. United States, 394 U.S. 165 (1969) — show that a technical trespass is sufficient to establish the existence of a search, but they provide little support.

In Soldal, the Court held that towing away a trailer home without the owner’s consent constituted a seizure even if this did not invade the occupants’ personal privacy. But in the present case, the Court does not find that there was a seizure, and it is clear that none occurred.

In Alderman, the Court held that the Fourth Amendment rights of homeowners were implicated by the use of a surreptitiously planted listening device to monitor third-party conversations that occurred within their home. See 394 U.S., at 176-180. Alderman is best understood to mean that the homeowners had a legitimate expectation of privacy in all conversations that took place under their roof. See Rakas, 439 U.S., at 144, n. 12 (citing Alderman for the proposition that “the Court has not altogether abandoned use of property concepts in determining the presence or absence of the privacy interests protected by that Amendment”); 439 U.S., at 153 (Powell, J., concurring) (citing Alderman for the proposition that “property rights reflect society’s explicit recognition of a person’s authority to act as he wishes in certain areas, and therefore should be considered in determining whether an individual’s expectations of privacy are reasonable); Karo, supra, at 732 (Stevens, J., concurring in part and dissenting in part) (citing Alderman in support of the proposition that “a homeowner has a reasonable expectation of privacy in the contents of his home, including items owned by others”).

In sum, the majority is hard pressed to find support in post-Katz cases for its trespass-based theory.

III
Disharmony with a substantial body of existing case law is only one of the problems with the Court’s approach in this case.

I will briefly note four others. First, the Court’s reasoning largely disregards what is really important (the use of a GPS for the purpose of long-term tracking) and instead attaches great significance to something that most would view as relatively minor (attaching to the bottom of a car a small, light object that does not interfere in any way with the car’s operation). Attaching such an object is generally regarded as so trivial that it does not provide a basis for recovery under modern tort law. See Prosser & Keeton §14, at 87 (harmless or trivial contact with personal property not actionable); D. Dobbs, Law of Torts 124 (2000) (same). But under the Court’s reasoning, this conduct may violate the Fourth Amendment. By contrast, if longterm monitoring can be accomplished without committing a technical trespass — suppose, for example, that the Federal Government required or persuaded auto manufacturers to include a GPS tracking device in every car — the Court’s theory would provide no protection.

Second, the Court’s approach leads to incongruous results. If the police attach a GPS device to a car and use the device to follow the car for even a brief time, under the Court’s theory, the Fourth Amendment applies. But if the police follow the same car for a much longer period using unmarked cars and aerial assistance, this tracking is not subject to any Fourth Amendment constraints.

In the present case, the Fourth Amendment applies, the Court concludes, because the officers installed the GPS device after respondent’s wife, to whom the car was registered, turned it over to respondent for his exclusive use. See ante, at 8. But if the GPS had been attached prior to that time, the Court’s theory would lead to a different result. The Court proceeds on the assumption that respondent “had at least the property rights of a bailee,” ante, at 3, n. 2, but a bailee may sue for a trespass to chattel only if the injury occurs during the term of the bailment. See 8A Am. Jur. 2d, Bailment §166, pp. 685-686 (2009). So if the GPS device had been installed before respondent’s wife gave him the keys, respondent would have no claim for trespass — and, presumably, no Fourth Amendment claim either.

Third, under the Court’s theory, the coverage of the Fourth Amendment may vary from State to State. If the events at issue here had occurred in a community property State4 or a State that has adopted the Uniform Marital Property Act,5 respondent would likely be an owner of the vehicle, and it would not matter whether the GPS was installed before or after his wife turned over the keys. In non-community-property States, on the other hand, the registration of the vehicle in the name of respondent’s wife would generally be regarded as presumptive evidence that she was the sole owner. See 60 C. J. S., Motor Vehicles §231, pp. 398-399 (2002); 8 Am. Jur. 2d, Automobiles §1208, pp. 859-860 (2007).

Fourth, the Court’s reliance on the law of trespass will present particularly vexing problems in cases involving surveillance that is carried out by making electronic, as opposed to physical, contact with the item to be tracked. For example, suppose that the officers in the present case had followed respondent by surreptitiously activating a stolen vehicle detection system that came with the car when it was purchased. Would the sending of a radio signal to activate this system constitute a trespass to chattels? Trespass to chattels has traditionally required a physical touching of the property. See Restatement (Second) of Torts §217 and Comment e (1963 and 1964); Dobbs, supra, at 123. In recent years, courts have wrestled with the application of this old tort in cases involving unwanted electronic contact with computer systems, and some have held that even the transmission of electrons that occurs when a communication is sent from one computer to another is enough. See, e.g., CompuServe, Inc. v. Cyber Promotions, Inc. 962 F. Supp. 1015, 1021 (SD Ohio 1997); Thrifty-Tel, Inc. v. Bezenek, 46 Cal. App. 4th 1559, 1566, n. 6 (1996). But may such decisions be followed in applying the Court’s trespass theory? Assuming that what matters under the Court’s theory is the law of trespass as it existed at the time of the adoption of the Fourth Amendment, do these recent decisions represent a change in the law or simply the application of the old tort to new situations?

IV

A
The Katz expectation-of-privacy test avoids the problems and complications noted above, but it is not without its own difficulties. It involves a degree of circularity, see Kyllo, 533 U.S., at 34, and judges are apt to confuse their own expectations of privacy with those of the hypothetical reasonable person to which the Katz test looks. See Minnesota v. Carter, 525 U.S. 83, 97 (1998) (SCALIA, J., concurring). In addition, the Katz test rests on the assumption that this hypothetical reasonable person has a well-developed and stable set of privacy expectations. But technology can change those expectations. Dramatic technological change may lead to periods in which popular expectations are in flux and may ultimately produce significant changes in popular attitudes. New technology may provide increased convenience or security at the expense of privacy, and many people may find the tradeoff worthwhile. And even if the public does not welcome the diminution of privacy that new technology entails, they may eventually reconcile themselves to this development as inevitable.6

On the other hand, concern about new intrusions on privacy may spur the enactment of legislation to protect against these intrusions. This is what ultimately happened with respect to wiretapping. After Katz, Congress did not leave it to the courts to develop a body of Fourth Amendment case law governing that complex subject. Instead, Congress promptly enacted a comprehensive statute, see 18 U.S.C. §§2510-2522 (2006 ed. and Supp. IV), and since that time, the regulation of wiretapping has been governed primarily by statute and not by case law.7 In an ironic sense, although Katz overruled Olmstead, Chief Justice Taft’s suggestion in the latter case that the regulation of wiretapping was a matter better left for Congress, see 277 U.S., at 465-466, has been borne out.

B
Recent years have seen the emergence of many new devices that permit the monitoring of a person’s movements. In some locales, closed-circuit television video monitoring is becoming ubiquitous. On toll roads, automatic toll collection systems create a precise record of the movements of motorists who choose to make use of that convenience. Many motorists purchase cars that are equipped with devices that permit a central station to ascertain the car’s location at any time so that roadside assistance may be provided if needed and the car may be found if it is stolen.

Perhaps most significant, cell phones and other wireless devices now permit wireless carriers to track and record the location of users — and as of June 2011, it has been reported, there were more than 322 million wireless devices in use in the United States.8 For older phones, the accuracy of the location information depends on the density of the tower network, but new “smart phones,” which are equipped with a GPS device, permit more precise tracking. For example, when a user activates the GPS on such a phone, a provider is able to monitor the phone’s location and speed of movement and can then report back real-time traffic conditions after combining (“crowdsourcing”) the speed of all such phones on any particular road.9 Similarly, phone-location-tracking services are offered as “social” tools, allowing consumers to find (or to avoid) others who enroll in these services. The availability and use of these and other new devices will continue to shape the average person’s expectations about the privacy of his or her daily movements.

V
In the pre-computer age, the greatest protections of privacy were neither constitutional nor statutory, but practical. Traditional surveillance for any extended period of time was difficult and costly and therefore rarely undertaken. The surveillance at issue in this case — constant monitoring of the location of a vehicle for four weeks — would have required a large team of agents, multiple vehicles, and perhaps aerial assistance.10 Only an investigation of unusual importance could have justified such an expenditure of law enforcement resources. Devices like the one used in the present case, however, make long-term monitoring relatively easy and cheap. In circumstances involving dramatic technological change, the best solution to privacy concerns may be legislative. See, e.g., Kerr, 102 Mich. L. Rev., at 805-806. A legislative body is well situated to gauge changing public attitudes, to draw detailed lines, and to balance privacy and public safety in a comprehensive way.

To date, however, Congress and most States have not enacted statutes regulating the use of GPS tracking technology for law enforcement purposes. The best that we can do in this case is to apply existing Fourth Amendment doctrine and to ask whether the use of GPS tracking in a particular case involved a degree of intrusion that a reasonable person would not have anticipated.

Under this approach, relatively short-term monitoring of a person’s movements on public streets accords with expectations of privacy that our society has recognized as reasonable. See Knotts, 460 U.S., at 281-282. But the use of longer term GPS monitoring in investigations of most offenses impinges on expectations of privacy. For such offenses, society’s expectation has been that law enforcement agents and others would not — and indeed, in the main, simply could not — secretly monitor and catalogue every single movement of an individual’s car for a very long period. In this case, for four weeks, law enforcement agents tracked every movement that respondent made in the vehicle he was driving. We need not identify with precision the point at which the tracking of this vehicle became a search, for the line was surely crossed before the 4-week mark. Other cases may present more difficult questions. But where uncertainty exists with respect to whether a certain period of GPS surveillance is long enough to constitute a Fourth Amendment search, the police may always seek a warrant.11 We also need not consider whether prolonged GPS monitoring in the context of investigations involving extraordinary offenses would similarly intrude on a constitutionally protected sphere of privacy. In such cases, long-term tracking might have been mounted using previously available techniques.

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For these reasons, I conclude that the lengthy monitoring that occurred in this case constituted a search under the Fourth Amendment. I therefore agree with the majority that the decision of the Court of Appeals must be affirmed.

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1Although the record does not reveal the size or weight of the device used in this case, there is now a device in use that weighs two ounces and is the size of a credit card. Tr. of Oral Arg. 27.

2At common law, a suit for trespass to chattels could be maintained if there was a violation of “the dignitary interest in the inviolability of chattels,” but today there must be “some actual damage to the chattel before the action can be maintained.” W. Keeton, D. Dobbs, R. Keeton, & D. Owen, Prosser & Keeton on Law of Torts 87 (5th ed. 1984) (hereinafter Prosser & Keeton). Here, there was no actual damage to the vehicle to which the GPS device was attached.

3The Court suggests that something like this might have occurred in 1791, but this would have required either a gigantic coach, a very tiny constable, or both — not to mention a constable with incredible fortitude and patience.

4See, e.g., Cal. Family Code Ann. §760 (West 2004).

5See Uniform Marital Property Act §4, 9A U. L. A. 116 (1998).

6See, e.g., NPR, The End of Privacy http://www.npr.org/series/114250076/the-end-of-privacy (all Internet materials as visited Jan. 20, 2012, and available in Clerk of Court’s case file); Time Magazine, Everything About You Is Being Tracked — Get Over It, Joel Stein, Mar. 21, 2011, Vol. 177, No. 11.

7See Kerr, The Fourth Amendment and New Technologies: Constitutional Myths and the Case for Caution, 102 Mich. L. Rev. 801, 850-851 (2004) (hereinafter Kerr).

8See CTIA Consumer Info, 50 Wireless Quick Facts, http://www.ctia.org/consumer_info/index.cfm/AID/10323.

9See, e.g., The bright side of sitting in traffic: Crowdsourcing road congestion data, Google Blog, http://googleblog.blogspot.com/2009/08/bright-side-of-sitting-in-traffic.html.

10Even with a radio transmitter like those used in United States v. Knotts, 460 U.S. 276 (1983), or United States v. Karo, 468 U.S. 705 (1984), such long-term surveillance would have been exceptionally demanding. The beepers used in those cases merely “emit[ted] periodic signals that [could] be picked up by a radio receiver.” Knotts, 460 U.S., at 277. The signal had a limited range and could be lost if the police did not stay close enough. Indeed, in Knotts itself, officers lost the signal from the beeper, and only “with the assistance of a monitoring device located in a helicopter [was] the approximate location of the signal . . . picked up again about one hour later.” Id., at 278.

11In this case, the agents obtained a warrant, but they did not comply with two of the warrant’s restrictions: They did not install the GPS device within the 10-day period required by the terms of the warrant and by Fed. Rule Crim. Proc. 41(e)(2)(B)(i), and they did not install the GPS device within the District of Columbia, as required by the terms of the warrant and by 18 U.S.C. §3117(a) and Rule 41(b)(4). In the courts below the Government did not argue, and has not argued here, that the Fourth Amendment does not impose these precise restrictions and that the violation of these restrictions does not demand the suppression of evidence obtained using the tracking device. See, e.g., United States v. Gerber, 994 F. 2d 1556, 1559-1560 (CA11 1993); United States v. Burke, 517 F. 2d 377, 386-387 (CA2 1975). Because it was not raised, that question is not before us.

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