The Supreme Court’s recent decision in Carpenter v. United States continues to generate interest more than a month after its release. While the Court proclaimed its holding as narrow, its unprecedented recognition of an individual’s privacy interest in data held by third parties could signal important changes in privacy more generally.
Timothy Carpenter was convicted for his participation in a series of armed robberies. While investigating Carpenter, law enforcement obtained court orders for cell-site location information under the Stored Communications Act (SCA). The SCA requires a showing of “specific and articulable facts … that there are reasonable grounds to believe that the contents of a wire or electronic communication, or the records or other information sought, are relevant and material to an ongoing criminal investigation.”
The court orders requested cell-site location information for periods of 127 days from one cell phone carrier and seven days from another. The government’s expert witness at Carpenter’s trial explained that cell phone carriers log certain information each time a cell phone accesses the wireless network. Using this information, the government produced “maps that placed Carpenter’s phone near four of the charged robberies.”
Carpenter argued that the government’s seizure of his cell-site location information violated the Fourth Amendment because he had a reasonable expectation of privacy in the cell-site location information and because the government had not obtained a warrant supported by probable cause.
The Fourth Amendment protects against “unreasonable searches and seizures” of “persons, houses, papers, and effects.” In Katz v. United States, 389 U.S. 347, 351 (1967), the Supreme Court extended this protection to an individual’s “reasonable expectation of privacy,” beginning a lengthy line of cases testing the boundaries of privacy.
According to the majority opinion, Carpenter sits at the intersection of two sets of Fourth Amendment cases. The first, beginning with United States v. Jones, 565 U.S. 400 (2012), recognized an individual’s expectation of privacy in a long-term surveillance of physical location and movement. Before Jones, the Court had held that augmented visual surveillance, involving use of a beeper attached to a vehicle and resulting in the tracking of an individual’s movements, did not constitute a search. The Supreme Court held in Jones that the placement of a GPS tracking device on a car was a trespass, and thus the collection of 28 days of location data using that device was a Fourth Amendment search. More importantly, a collection of five concurrences in Jones agreed that “longer term GPS monitoring,” in certain circumstances, “impinges on expectations of privacy.” It is this agreement among the concurrences that forms the first pillar of the Court’s holding in Carpenter.
The second set of Fourth Amendment cases relates to what is commonly known as the third-party doctrine. That long-standing doctrine holds that an individual generally “has no legitimate expectation of privacy in information he voluntarily turns over to third parties.” The Court has applied the third-party doctrine in contexts as varied as bank records and pen registers (that is, records of dialed phone numbers). For example, in United States v. Miller, 425 U.S. 435 (1976), the Court rejected a Fourth Amendment challenge to the collection of bank records partly because the records were not confidential and contained information that was exposed to the bank as part of the bank’s business. Similarly, the Court has rejected a challenge to the use of a pen register because the dialed numbers are used by the telephone company.
The Supreme Court, by a 5–4 majority, agreed with Carpenter and held that the government’s acquisition of cell-site location information covering a period of seven days or more was a search under the Fourth Amendment. In doing so, the Court for the first time recognized an individual’s reasonable expectation of privacy in information generated and maintained by third parties in the course of business. The Court characterized the cell-site location information as “detailed, encyclopedic, and effortlessly compiled.” The Court emphasized that a comprehensive record of an individual’s movements was sufficiently different from bank records and pen register information to which the Court had previously applied the third-party doctrine.
As the Court made clear, the comprehensive nature of the information at issue was a key consideration in its decision. An “all-encompassing record of the holder’s whereabouts,” capable of revealing information about not only “particular movements” but also “familial, political, professional, religious, and sexual associations,” posed privacy concerns. The ubiquity of cell phone usage and the fact that the data in question was retrospective in nature also factored into the Court’s reasoning. Notably, the Court explicitly based its reasoning on the likelihood that cell-site location information would improve, amplifying the privacy concerns associated with unfettered access to such information.
The Court took pains to emphasize Carpenter’s limited Fourth Amendment application at great length: the decision does not address the real-time capture of cell-site location information (as opposed to retrospective collection), collection of cell-site location information covering a shorter period of time, or the capture of information on all devices that connected to a particular cell site during a particular time period. Nor does Carpenter itself upturn application of the third-party doctrine in other areas, such as for bank records or pen register information, or invalidate legal process standards under the SCA or ECPA. However, as the dissents make clear, Carpenter represents a substantial departure from existing precedent under the third-party doctrine.
The Carpenter decision departs substantially from previous Fourth Amendment doctrine, expanding individuals’ privacy interests in automatically and ubiquitously collected digital data held by third parties. Rather than apply the traditional bright-line rule that information given to a third-party loses Fourth Amendment privacy protection, the Court employed a kind of balancing test, focusing on the substance and nature of the information at issue along with the circumstances of its collection in determining whether individuals retained privacy interests in the information. By abandoning the previous bright-line rule, the Court invites substantial follow-on litigation with potentially broad applications.
Privacy interest in a “comprehensive record”
Carpenter signals a shift in the characterization of Fourth Amendment privacy interests. Rather than hinging Fourth Amendment protection on an individual’s “persons, houses, papers, and effects,” or on whether the information is a business record or has been disclosed to a third party, the Court’s decision weighs the sensitive nature of certain data—data that reveals the whole of a person’s physical movements. Regardless of whether a third party generates such information or “the Government employs its own surveillance technology” to generate it, the Court has for the first time held that an individual has a reasonable expectation of privacy in comprehensive records of their movements, even when those records are held by a third party.
Put differently, the Carpenter decision recognized an individual’s expectation of privacy in a comprehensive record of their movement generated and held by a third party, while the Jones concurrences recognized an individual’s expectation of privacy in a comprehensive record of their public movements tracked and compiled by the government through a GPS tracker. By its terms, the Fourth Amendment protects the right of individuals “to be secure in their persons, houses, papers, and effects.” In combination, the Carpenter decision and Jones concurrences imply that a comprehensive record of an individual’s movements constitutes a paper or effect that belongs to the individual even when the record is not within the individual’s possession and is not generated by the individual.
Privacy and the compilation of data
Carpenter continues the Court’s recent interest in the compilation of data and digital technologies, underscoring the rationale for establishing arguably separate standards for digital and non-digital data. In particular, Carpenter discusses the “detailed, encyclopedic, and effortlessly compiled” nature of the location information at issue, its “ability to chronicle a person’s past movements,” and the continued and ongoing improvements in the underlying technology. This discussion echoes the concurring opinions in Jones, which point to the wealth of information afforded by GPS monitoring and raise interesting questions about the broad array of data held by third parties and routinely compiled: phone numbers dialed or texted, URLs visited, emails exchanged, and even goods purchased. Along those lines, Riley v. California carved out an exception for digital data, protecting cellular telephones from being searched incident to arrest. According to the Court in Riley, the collection of “many distinct types of information” on cell phones raised unique privacy concerns.
Taken together, the Court’s recent jurisprudence shows an underlying concern with the unprecedented availability of large amounts of comprehensive data through digital technologies. The Court’s opinion in Carpenter abandons the traditional Fourth Amendment dividing line between private information and information held by third parties at least when huge volumes of digital data are generated, compiled, and stored automatically. Likewise, five Justices in Jones recognized a privacy interest even when location information is exposed to the public if it covers a sufficient length of time. And in Riley, the Court held that the nature and quantity of data on cell phones today is too great to fall under the rubric of a traditional warrantless arrest search. Digital, the Court is telling us, is different.
The Court’s reasoning carries significance for privacy in the digital age. As a starting point, Carpenter portends only the beginning, rather than the end, of litigation concerning the third-party doctrine as it relates to digital data. While Carpenter focuses on a person’s expectation of privacy in a comprehensive record of the person’s movements, it is easy to imagine other scenarios in which the compilation of data exposed to the public or maintained by third parties produces similarly sensitive records. And as Justice Sotomayor’s concurrence in the Jones case points out, we should not assume that an individual lacks an expectation of privacy in, for example, a comprehensive web browsing history or other online activities. More generally, Carpenter comes at a time of potential upheaval in the privacy space. Carpenter’s ramifications will be litigated heavily at the state and federal levels, and its fallout may greatly interest legislators and privacy advocates in this country and elsewhere.
 Carpenter, 585 U. S. ____ (2018) (slip op., at 4).
 18 U.S.C. § 2703(d).
 Carpenter, 585 U. S. ____ (slip op., at 3). Note that the request for seven days of cell-site location information yielded only two days’ worth of data.
 Id. at 3-4.
 Id. at 3.
 United States v. Knotts, 460 U. S. 276 (1983).
 United States v. Jones, 565 U.S. 400, 404 (2012)
 Id. at 430 (ALITO, J., concurring in judgement); id., at 415 (SOTOMAYOR, J., concurring).
 Smith v. Maryland, 442 U.S. 735, 743-744 (1979).
 Id. at 742.
 Carpenter, 585 U. S. ____ (slip op., at 10).
 Id. at 11.
 Id. at 12.
 Id. at 12-13.
 Id. at 14.
 Id. at 17-18.
 Carpenter, 585 U. S. ____ (slip op., at 7) (KENNEDY, J., dissenting).
 Carpenter, 585 U. S. ____ (slip op., at 11).
 Carpenter, 585 U. S. ____ (slip op., at 10).
 See Jones, 565 U.S. 400, 428 (SOTOMAYOR, J., concurring).
 Riley v. California, 573 U.S. __ , __ (2014) (slip op., at 18).
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