The Supreme Court is set to hear Carpenter v. United States on November 29, 2017.1 The question presented to the Court is whether the government violates an individual’s Fourth Amendment rights by collecting historical cell-site location information without a warrant.

The District Court for the Eastern District of Michigan convicted Timothy Carpenter of armed robberies in violation of the Hobbs Act, among other charges, and the Sixth Circuit Court of Appeals affirmed the conviction, holding that the government did not conduct a “search” for Fourth Amendment purposes when it obtained cell tower locational data records from Carpenter’s wireless carriers.2 Privacy advocates hope that this case will push the Court into framing a rule that is adaptable to rapid technological advancement in surveillance under the Fourth Amendment.3

In April 2011, Detroit police arrested four men suspected of robbing Radio Shack and T-Mobile stores in the Detroit metro area.4 When one of the suspected robbers confessed, police received his cellphone and the cellphone numbers of other alleged participants.5 Soon after, the FBI applied for three magistrate orders for the “transactional records” from the wireless carriers.6 Under the order, the FBI requested subscriber information, toll records, and call detail records, including listed and unlisted numbers dialed or otherwise transmitted to and from the targeted phones for a historical 127-day period, as well as “cell site information for the target telephones at call origination and termination for incoming and outgoing calls.”7

The magistrates approved the application under the Stored Communications Act, which allows authorities to require the disclosure of telecommunication records when “specific and articulable facts show that there are reasonable grounds to believe that the contents of a wired or electronic communication, or the records or other information sought, are relevant and material to an ongoing criminal investigation.”8 Without a warrant, the FBI gathered historical cell-site locational information showing that Carpenter had used his phones within a half-mile to two-mile radius of the respective robberies.

Carpenter moved to suppress the government’s cell-site evidence on Fourth Amendment grounds, arguing that the records could be seized only with a warrant supported by probable cause.9 The government argued that a “person has no Fourth Amendment interest in records created by a communications service provider in the ordinary course of business that pertain to the individual’s transactions with the service provider.”10

Many privacy scholars believe this will be the most important privacy case in a generation.11 The importance of the case does not hinge on cell-site location information, rather, the Court will need to decide “where to draw lines in terms of what network surveillance triggers the Fourth Amendment and how the Fourth Amendment applies.”12

The reasonable expectation of privacy test is the predominant test for whether the government violated the Fourth Amendment. The test uses the two-pronged analysis outlined by Justice Harlan that looks to the subjective expectation of privacy of the defendant and whether that expectation is one society is prepared to recognize as reasonable.13

Under this test, traditional Fourth Amendment analysis in situations similar to Carpenter would require evaluating the government’s conduct under either the third-party doctrine or the mosaic theory. The third-party doctrine, as seminally described in Smith v. Maryland, finds that individuals who voluntarily provide third parties with information, whether phone companies or internet service providers, have no reasonable expectation of privacy in that information.14 The Sixth Circuit found that Carpenter had no reasonable expectation of privacy in his cell-site locational data because it was voluntarily provided to his cellular service provider.15

As an alternative to the third-party doctrine, scholars such as Kerr have expounded the mosaic theory. Under the mosaic theory, courts evaluate the “collective sequence of government activity as an aggregated whole to consider whether the sequence amounts to a search.”16 In Carpenter, the Court would evaluate the process by which the government collected the information about Carpenter to determine whether they violated his Fourth Amendment rights. For example, it may evaluate what information was gathered and for how long that information was gathered without a warrant. The Court may also ask if cell-site locational data was too invasive, or if the 127 days of gathering was excessive.

In Jones, Justice Alito’s concurring opinion found that a search had occurred because a continuous twenty-eight-day use of GPS to monitor a drug suspect’s vehicular movements violated a reasonable expectation of privacy.17 He explained that without the GPS technology, a month of surveillance with traditional methods—such as physically tailing the suspect—would have been impractical, causing a strain on law enforcement resources.18 Thus, under Justice Alito’s rationale, society would certainly find the 127 days of data collection from Carpenter unreasonable under the second prong of the Katz privacy test.

As privacy scholars such as Kerr and Vladeck have noted, Carpenter allows the Court—now with Justice Gorsuch—to address the future of the Fourth Amendment and push in one of three directions19: it could apply the reasonable expectation of privacy test; it could adopt a mosaic theory test similar to the one described above; or it could also draw a bright line for when and how much cell-site (historical or prospective) data law enforcement may collect without a warrant. Justice Gorsuch, while a judge on the Tenth Circuit, applied the reasonable expectation of privacy test for Fourth Amendment analysis.20 If that is a significant indicator, then the Court will likely push in that direction given its ideological makeup. The mosaic theory, while comprehensive, will not likely have enough support with Justice Gorsuch on the bench. The third option, a bright line for law enforcement data collection, could be the most practical and helpful solution. However, it seems to be only a remote possibility given the precedent of the Court.

The stakes are important here. As technology marches on at a rapid pace, and as Americans become more attached to their technological devices, individuals have accumulated tremendous amounts of data. The Court’s decision here will determine whether the government will seek a warrant to access data based on probable cause or whether they will have free rein to search your records and electronic information without a warrant.