Since Steve Jobs unveiled the legendary iPhone in 2007, smartphones have fundamentally changed countless aspects of human interaction from how we navigate to how we communicate. Today, over three-quarters of adults in the United States own a smartphone, making it one of the fastest spreading technologies of all time. The emergence of smartphones has also changed the way federal and local law enforcement agencies conduct investigations using data-collecting techniques that some argue infringe on our right to privacy.

On November 29th, the Supreme Court heard oral arguments in a case which lies at the intersection of the ever-evolving capabilities of technology and the decades-old Fourth Amendment doctrine. The issue in Carpenter v. United States is whether police obtaining historical cell-site records that reveal time-stamped locations of a cell phone user without a warrant is permitted under the Fourth Amendment.

The case arose from the conviction of a man named Timothy Carpenter, who was involved in a series of armed robberies in which a group of men targeted cell phone stores in Michigan. Ironically, it was Carpenter’s own cell phone that ultimately led to his conviction and life sentence. Carpenter acted as the leader of the group, supplying the guns and signaling the start of each robbery. After a coconspirator confessed to the robberies and turned over Carpenter’s phone number, the government applied for historical cell-site records under the Stored Communications Act. Unlike the probable cause requirement for obtaining a warrant under the Fourth Amendment, the Stored Communications Act merely states that a court order may be issued if there are “reasonable grounds to believe” that the information sought is relevant and material to a criminal investigation. The court order was granted, and the government received four months of cell-site location data, which placed Carpenter near several of the robberies in question and ultimately contributed to his conviction.

On appeal, a divided three-judge panel on the Sixth Circuit affirmed Carpenter’s conviction and sentence, holding that the government collection of cell-site location data from cell service providers did not require a warrant, because it did not constitute a search under the Fourth Amendment. The test for a Fourth Amendment search comes from Justice Harlan’s concurring opinion in Katz v. United States (1967). Under the two-part Katz test, a search requires a warrant if the individual has a subjective expectation of privacy that “society is prepared to recognize as reasonable.” In the 1979 case Smith v. Maryland, the Supreme Court explored how this test applied in the context of phone records: the police had installed a pen register at a central telephone company office to record telephone numbers dialed from the suspect’s home phone. The Court stated that obtaining a record of phone numbers from a suspect is not a search under the Fourth Amendment, because an individual has “no legitimate expectation of privacy in information he voluntarily turns over to third parties.” The Sixth Circuit reasoned that under this third-party doctrine, Carpenter voluntarily carried and used his cell phone, and he therefore lacked a sufficient interest in the cell-site records created and maintained by his wireless carriers.

Carpenter v. United States illustrates the fundamental conflict between rapidly evolving technology and relatively static constitutional doctrine. The legitimate expectation of privacy standard articulated in Smith is incompatible with how technology, particularly the smartphone, is used in everyday life. As Justice Sotomayor pointed out in her concurrence in the 2012 case United States v. Jones, “[t]his approach is ill-suited to the digital age, in which people reveal a great deal of information about themselves to third parties in the course of carrying out mundane tasks.” Hopefully, the Supreme Court will use Carpenter v. United States to readdress the third-party doctrine and articulate a Fourth Amendment standard that is more closely aligned with our privacy expectations today.