On June 22, the Supreme Court issued its highly anticipated decision addressing privacy in the digital age, holding that the government generally must obtain a search warrant supported by probable cause to search a target’s historical cell site location information (CSLI), which can provide a detailed record of an individual’s whereabouts. In siding with the petitioner, Timothy Carpenter, who was convicted and sentenced to prison based largely on 127 days of CSLI that placed him near the scene of a string of armed robberies, the Court confirmed that individuals have an expectation of privacy in their historical CSLI that is protected by the Fourth Amendment. Writing for the majority, Chief Justice Roberts spurned mechanical applications of traditional Fourth Amendment doctrine, preferring instead to endorse a more flexible and nuanced approach to privacy in the digital age, where rapidly advancing technologies threaten to erode privacy protections.

Underlying the Court’s decision was the recognition that cellphones have become “indispensable to participation in modern society” and that “seismic shifts in digital technology” now allow wireless carriers to collect “deeply revealing” information about cellphone users. In holding that law enforcement officials generally need a search warrant in order to obtain CSLI records, the Court refused to extend two long-standing lines of Fourth Amendment precedent to the digital age. In the first line of cases, the Court had ruled that individuals generally should not expect their physical location to be protected from law enforcement surveillance. For example, a driver should not expect her movements on public roads to be kept private. However, in 2012, the Court decided in United States v. Jones that law enforcement officers needed a warrant to install a GPS tracking device on a subject’s car. The Carpenter decision expressed concern that historical CSLI presented an even greater invasion of privacy than did GPS monitoring, because people carry their cellphones virtually everywhere, noting that:

Mapping a cell phone’s location over the course of 127 days provides an all-encompassing record of the holder’s whereabouts. As with GPS information, the timestamped data provides an intimate window into a person’s life, revealing not only his particular movements, but through them his “familial, political, professional, religious and sexual associations”. . . .These location records hold for many Americans the ‘privacies of life.’”

In the second line of precedent rejected by Carpenter, the Court had previously ruled that individuals did not have an expectation of privacy for information in the possession of a third party. Under this “third-party doctrine,” law enforcement routinely obtains records without a search warrant from telecommunications companies concerning the telephone numbers of calls dialed and received and from banks and credit card companies. In refusing to extend this line of reasoning to cellphone location records, the Carpenter Court expanded upon its recent holding from Riley v. California (2014), where the unanimous Court held the warrantless search of the digital content of a cellphone unconstitutional because cellphones “differ in both a quantitative and a qualitative sense from other objects” that people carry with them, given their immense storage capacity for information revealing “the sum of an individual’s private life.”

Despite Carpenter’s emphasis that the government must get a warrant to obtain records protected by the Fourth Amendment in the hands of third parties, the Court suggested that, ultimately, such circumstances would be rare, stating, “The Government will be able to use subpoenas to acquire records in the overwhelming majority of investigations.” Moreover, the Court made clear that the ruling should be narrowly construed to the facts of the case, and declined to extend its ruling to “conventional surveillance techniques and tools, such as security cameras” or “business records that might incidentally reveal location information.” In addition, the Court allowed some room for warrantless searches on historical CSLI under certain exigent circumstances, including the need to pursue a fleeing suspect, protect individuals from imminent harm and prevent the destruction of evidence. Notably, the Court left open the possibility that historical CSLI for a period of less than seven days might be obtained without need for a warrant.

The Carpenter case drew considerable interest from a number of leading technology companies, as well as civil rights advocates, privacy think tanks and criminal defense organizations. The tech company amicis was eager to point out that it has made extensive efforts to limit government access to its records, absent the proper showing, while providing greater transparency to customers regarding those requests. With the rapid growth in utilization of network-connected, “internet of things” technologies that collect comprehensive digital troves of information about individuals simply as a consequence of their operation, these service providers appealed for more flexible frameworks for handling government requests in the future.

The Court’s reasoning in Carpenter reflects an evolution in Fourth Amendment doctrine that recognizes the nature of these revolutionary advances in technology and corresponding changes in societal privacy expectations. However, by limiting its holding to address only historical CSLI, the ever-cautious Supreme Court has left room for lower courts and Congress to address privacy concerns related to other types of personal digital data.