Is your cell phone nearby? Are you reading this article on it right now? It’s probably no surprise to you that Americans are with their cell phones constantly. And, you may already know that your cell phone is constantly scanning for the best signal. What you may not know is that in the process, your cell phone connects to cell sites and generates a time-stamped record of that connection: cell-site location information (CSLI). That CSLI tells a story about all of your comings and goings, tracing back up to five years. In a landmark decision issued this term, Carpenter v. United States, No. 16-402 (June 22, 2018), the Supreme Court held that the government’s access of CSLI was a search under the Fourth Amendment and, therefore, required a warrant.
Carpenter involved a criminal defendant whose movements over approximately three months were captured by CSLI held by two cell phone service providers. The government obtained that data from the providers (without a warrant) and used it to help convict the defendant of robbery, pointing out that he was physically close to four of the robberies while they were taking place, and relying on his CSLI to do so.
In the past, the Supreme Court has held that there is no reasonable expectation of privacy in information voluntarily shared with third parties. That’s common sense—if one posts a yard sign saying “I robbed the bank,” I don’t have a reasonable expectation that the information would stay private. Likewise, it wouldn’t be a “search” if a police officer stood outside one’s house and read the sign.
But the Supreme Court concluded that CSLI is different. Not only are cell phones “indispensable to participation in modern society,” the Court said, apart from disconnecting one’s phone entirely, there is no way to avoid leaving behind the trail of location data. Could anyone really be said to voluntarily assume the risk of turning over what the Court called a “comprehensive dossier” of one’s physical movements? The Carpenter majority didn’t think so. Peering into the vast trove of location data stored by cell phone providers constituted a “search” in the Court’s eyes, and a warrant would be needed as a consequence. That’s a relief for the millions of Americans who—as the Court cheekily observed in another case—see their cell phone as “a feature of human anatomy.”
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