Most Americans carry a cellphone with them at all times. Little do they know that they are constantly transmitting information about their whereabouts to their phone service provider. In November, the U.S. Supreme Court heard oral argument in Carpenter v. United States, a case that will determine whether the Fourth Amendment allows the government to access an individual's cellphone location records without a warrant.

This case began with the arrest of Timothy Carpenter, who orchestrated a number of robberies in Ohio and Michigan. Based on information from Carpenter's co-conspirators, the government obtained a court order—not a warrant—requiring Carpenter's cellphone carrier to provide 127 days of location records for Carpenter's account. These records provided the location of the cellphone towers with which Carpenter's cellphone connected at the time he made calls. Relying on these records, the government determined that Carpenter's cellphone connected with towers in the vicinity of several of the robberies at approximately the same time as those robberies. Given that cellphones connect with the tower to which they are closest at the time of the call, this was compelling evidence in the government's prosecution.

Prior to trial, Carpenter unsuccessfully moved to suppress the government's use of his cellphone location records under the Fourth Amendment. A jury convicted Carpenter on numerous counts of the Hobbs Act and firearms charges. The U.S. Court of Appeals for the Sixth Circuit affirmed his conviction, rejecting Carpenter's renewed argument that the government violated his Fourth Amendment rights by its warrantless search of his cellphone location records.

In asking the Supreme Court to overturn his conviction, Carpenter presented a two-part argument. First, Carpenter argued that the government's acquisition of cellphone location records constitutes a search under the Fourth Amendment because individuals have a reasonable expectation of privacy in the geo-location data emitted by their cellphones. Carpenter argued that this case was not governed by the “third party doctrine”—which dictates that the Fourth Amendment offers no protection for information that an individual voluntarily shares with a third party—both because cellphone location records are more sensitive that the records at issue in the court's previous cases (bank records and telephone numbers) and also because cellphone users do not voluntarily share this information. Second, Carpenter argued that the warrantless search of his cellphone location records was unreasonable. Carpenter reasoned that he has a compelling privacy interest in his cellphone records because he keeps his cellphone with him at all times and, therefore, these records provide constantly updated information on his location, even when he is in his own home or in other locations where he would have a reasonable expectation of privacy.

The government argued that the use of Carpenter's cellphone location records did not violate his Fourth Amendment rights. The government posited that its acquisition of Carpenter's cellphone location records did not constitute a Fourth Amendment search. In support of this argument, the government relied on the third party doctrine and maintained that Carpenter had no legitimate expectation of privacy in these records. Additionally, the government argued that Carpenter maintained no ownership interest in his cellphone location records because the carrier collected these records in the ordinary course of business.

At oral argument, the justices seemed keenly aware of the difficulty in drawing privacy lines in an age of increasingly ubiquitous and invasive technology. Justice Stephen Breyer may have said it best when he referred to the advancements in technology as “an open box” and remarked that the court knows “not where to go.” Justices Sonia Sotomayor and Neil Gorsuch, perhaps regarded as unlikely allies, both expressed a visceral concern that the government would violate basic principles of privacy enshrined in the Fourth Amendment by tracking the location of cellphone users. By contrast, Justice Anthony Kennedy appeared unmoved by privacy concerns when he commented that most cellphone users know that their carrier collects geo-location data.

Questions posed by Justice Elena Kagan and Chief Justice John Roberts focused on inconsistencies between the government's position and the court's prior rulings. Justice Kagan asked the government to distinguish the facts in this case from those in United States v. Jones, where the court held that attaching a GPS device to a car constitutes a search under the Fourth Amendment. In response to Kagan's request, the government argued that, unlike GPS data, cellphone location records are developed by a phone carrier as a business record. Kagan appeared unpersuaded by this argument. Likewise, Chief Justice Roberts remarked that he viewed the government's position as inconsistent with the holding of Riley v. California, in which the justices ruled that the government may not conduct a warrantless search of an arrestee's cellphone.

The justices appeared to be conflicted about whether the third party doctrine should apply in this case. Justice Samuel Alito suggested that bank records—which the court has allowed the government to obtain without a warrant—are potentially far more sensitive than cellphone location records. Justice Kennedy echoed Justice Alito's sentiment, noting that cellphone location records only reveal movements that could otherwise be publicly viewed. By contrast, Sotomayor and Breyer seemed poised to find cellphone location records to be uniquely revealing and therefore exempt from the third party doctrine.

Given the centrality of cellphones in everyday life, Carpenter may be one of the Supreme Court's most important Fourth Amendment decisions in recent memory. A decision is expected in early summer 2018.

Stephen A. Miller practices in the commercial litigation group at Cozen O'Connor's Philadelphia office. Prior to joining the firm, he clerked for Justice Antonin Scalia on the U.S. Supreme Court and served as a federal prosecutor for nine years in the Southern District of New York and the Eastern District of Pennsylvania.

Rachel Collins Clarke also practices in the firm's commercial litigation group. Prior to joining the firm, she served as an assistant district attorney in Philadelphia and graduated from Georgetown University Law Center.