In a time when the number of U.S. cell phones is bigger than the number of U.S. citizens, the Supreme Court took a major step toward defending the privacy of the millions of cell phone users in the United States. In Carpenter v. United States, a 5-to-4 decision on June 22, 2018, the Court ruled that a warrant is generally required to gain access to cell phone location data. The ruling goes a long way towards ensuring Americans’ Fourth Amendment rights, which protect individuals from unreasonable search and seizure.
As GPS trackers and cell phones have risen to figure more and more prominently into Americans’ daily lives, so too has risen a need to determine just how these powerful devices fit within the framework of the Constitution, as well as how to guarantee that their owners retain their privacy. In 2012, the Court ruled that a warrant is required for police to use a GPS tracker to track a suspect’s movements, and in 2014, the Supreme Court held that a warrant is required to search cell phones—police cannot search through a phone simply because the phone’s owner was arrested.
With Carpenter, the Court expressed further reluctance to allow unlimited governmental access to digital data. Writing for the majority, Chief Justice Roberts noted that digital data can provide a look into an individual’s private affairs so “comprehensive, detailed, and intrusive” that it would have been impossible to imagine not long ago. However, the ruling is limited. The Court held that a warrant is required only “in the rare case where the suspect has a legitimate privacy interest in records held by a third party,” and that “an individual maintains a legitimate expectation of privacy in the record of his physical movements as captured through CSLI [Cell-Site Location Information].” The result is that authorities will typically need warrants to access cell phone location information, but the Court left open the question of whether warrants were necessary to obtain information such as real-time cell tower data.
CSLI can capture incredibly detailed information about a person’s day-to-day life—so detailed that Justice Roberts equated the government’s tracking of a cell phone’s location to “attach[ing] an ankle monitor to the phone’s user”—and amassing such data would have seemed impossible perhaps as little as forty years ago. The Supreme Court’s ruling in Carpenter serves as a clear indication that the rules governing the use of technology will have to evolve just as quickly as the technology itself.