SEPARATE OPINIONS
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 406-407, n. 3, 181 L. Ed. 2d, at 919. In this case, the Government installed a *924Global 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, F ourth
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Amendment protection. See, e.g., Silverman v. United States, 365 U.S. 505, 511-512, 81 S. Ct. 679, 5 L. Ed. 2d 734 (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, 121 S. Ct. 2038, 150 L. Ed. 2d 94 (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, 121 S. Ct. 2038, 150 L. Ed. 2d 94; see also Smith v. Maryland, 442 U.S. 735, 740-741, 99 S. Ct. 2577, 61 L. Ed. 2d 220 (1979); Katz v. United States, 389 U.S. 347, 361, 88 S. Ct. 507, 19 L. Ed. 2d 576 (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, 88 S. Ct. 507, 19 L. Ed. 2d 576. 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 409, 181 L. Ed. 2d, at 920. 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, 103 S. Ct. 1081, 75 L. Ed. 2d 55 (1983) (Brennan, J., concurring in judgment); see also, e.g., Rakas v. Illinois, 439 U.S. 128, 144, n. 12, 99 S. Ct. 421, 58 L. Ed. 2d 387 (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 422-424, 181 L. Ed. 2d, at 929-930 (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
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426-429, 181 L. Ed. 2d, at 931-933. 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 bans). 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 *925analysis.” Ante, at 411, 181 L. Ed. 2d, at 922. As Justice Alito incisively observes, the same technological advances that have made possible non-trespassory surveillance techniques will also affect the Katz test by shaping the evolution of societal privacy expectations. Post, at 428, 181 L. Ed. 2d, at 933. 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 430, 181 L. Ed. 2d, at 934.
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
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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, 124 S. Ct. 885, 157 L. Ed. 2d 843 (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, 121 S. Ct. 2038, 150 L. Ed. 2d 94; ante, at 412, 181 L. Ed. 2d, at 923 (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 coordi*926nate branch, a tool so amenable to misuse, especially in light of the Fourth Amendment’s goal to curb arbitrary exercises of police power and prevent “a
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too permeating police surveillance,” United States v. Di Re, 332 U.S. 581, 595, 68 S. Ct. 222, 92 L. Ed. 210 (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, 99 S. Ct. 2577, 61 L. Ed. 2d 220; United States v. Miller, 425 U.S. 435, 443, 96 S. Ct. 1619, 48 L. Ed. 2d 71 (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,
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at 427, 181 L. Ed. 2d, at 932, 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, 99 S. Ct. 2577, 61 L. Ed. 2d 220 (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, 88 S. Ct. 507, 19 L. Ed. 2d 576 (“[W]hat [a person] seeks to preserve as private, even in an area ac*927cessible 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.
United States v. Knotts, 460 U.S. 276, 103 S. Ct. 1081, 75 L. Ed. 2d 55 (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 409, n. 6, 181 L. Ed. 2d, at 920 (quoting 460 U.S., at 284, 103 S. Ct. 1081, 75 L. Ed. 2d 55).
United States v. Karo, 468 U.S. 705, 104 S. Ct. 3296, 82 L. Ed. 2d 530 (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, 104 S. Ct. 3296, 82 L. Ed. 2d 530. 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.eom/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, 104 S. Ct. 3296, 82 L. Ed. 2d 530. A car’s movements, by contrast, are its owner’s movements.