In 2011, Detroit police obtained records from Timothy Carpenter’s cellular service provider showing the movements of his cell phone.  From those records, they were able to track Carpenter’s whereabouts over a four-month period. Based in part on information obtained from those records, Carpenter was convicted of six different robberies.  Carpenter appealed to the Sixth Circuit Court of Appeals, where he argued that the government violated his rights under the Fourth Amendment by obtaining and examining those records. The court ruled for the government, concluding that Carpenter had no reasonable expectation of privacy in cell phone location records.  Carpenter asked the Supreme Court to hear the case, and it agreed to do so.

CAC filed a friend-of-the-court brief in the Supreme Court on behalf of scholars of the history and original meaning of the Fourth Amendment, arguing that the government violated Carpenter’s Fourth Amendment right to be protected from unreasonable searches and seizures. As we explained, obtaining and examining Carpenter’s cell phone records was a “search” in any normal sense of the word, and it is a “search” within the meaning of the Fourth Amendment.  Further, we explained that entrusting government agents with unfettered discretion to conduct searches using cell site location information undermines the Fourth Amendment “right of the people to be secure . . . against unreasonable searches.”  Indeed, although the Framers of the Fourth Amendment could not have anticipated cell-phone technology, they deliberately chose language that demonstrated their recognition of the dangers inherent in any state claim of unlimited authority to conduct searches for evidence of criminal activity. Finally, although there is a federal law called the Stored Communications Act that imposes some limits on the government’s access to certain information in cell phone records, that Act was enacted long before access to telephone records allowed comprehensive tracking of subscribers’ movements, and, as a consequence, it does not require sufficiently rigorous justifications for government access to this revealing data.

The Supreme Court held that the government’s acquisition of Carpenter’s cell phone location records constituted a search, and that the government should have first obtained a warrant. Echoing our brief, Chief Justice Roberts, writing for the Court, discussed the history underlying the Fourth Amendment and explained that “a central aim of the Framers was ‘to place obstacles in the way of a too permeating police surveillance.’”  He also made clear that “the Court is obligated . . .  to ensure that the ‘progress of science’ does not erode Fourth Amendment Protections” and that “granting the state unrestricted access to a wireless carrier’s database of physical location information” would “risk[] Government encroachment of the sort the Framers . . . drafted the Fourth Amendment to prevent.”