Does the constitution permit police to track your phone signal without a warrant?
TIMOTHY CARPENTER, a Michigan man, had a habit of stealing smartphones from Radio Shacks and T-Mobile stores; his own phone provided the evidence authorities needed to nab him. On June 5th, the Supreme Court agreed to hear Mr Carpenter’s complaint that his privacy rights under the Fourth Amendment were violated when his phone company shared data on his whereabouts with law-enforcement agents. This ill-gotten information, he says, should never have been introduced at his trial. When the justices return to work in the autumn (after a break that begins in July), they will consider Carpenter v United States and puzzle over the implications of an 18th-century rule for a distinctly 21st-century reality.
In 2011, when Mr Carpenter was arrested for organising a series of armed robberies in Michigan and Ohio, the FBI built its case on 127 days of historical cell tower data showing where he was at the times when the crimes took place. This information was retrieved under the Stored Communications Act, a law permitting phone companies to divulge information when there are “specific and articulable facts” that are “relevant and material” to a criminal investigation. By placing Mr Carpenter within a stone’s throw of the robberies based on the cell towers through which he placed and received calls, the FBI was able to map his movements and convict him. He is now serving consecutive sentences adding up to 116 years.
When the Fourth Amendment was ratified in 1791, the “right of the people to be secure in their persons, house, papers and effects” was designed as a bulwark against “general warrants”—licence for authorities to search anything and everything in somebody’s home. Searches and seizures cannot be “unreasonable”, the amendment said. Over the years, the Supreme Court has tried to clarify this rather amorphous standard. Most searches require “probable cause”—a reasonable belief that someone has broken a particular law. And generally, authorities need a judge to issue a targeted search warrant if probable cause exists. But there are exceptions to this rule, and the Sixth Circuit Court of Appeals thought Mr Carpenter’s case was one. Cell-tower data is mundane information phone companies gather to monitor the strength of their networks and track roaming charges, the court held. Mr Carpenter could not have expected that such information about his phone calls was a secret.
In 2014, when mobile phones were last on the docket in Riley v California, the Supreme Court said that police needed a warrant to search a suspect’s smartphone. These devices contain “[t]he sum of an individual’s private life…from the mundane to the intimate”, Chief Justice John Roberts wrote, and could be more revealing than “the most exhaustive search of a house.” But the Fourth Circuit noted a significant distinction between searching a phone and gleaning the general location of an individual based on which direction his phone pings. The cell-tower data only tells whether someone “happens to be located within a two-mile radial wedge”.
In their plea to the justices, Mr Carpenter’s lawyers urged the court to “re-examine traditional notions of privacy in the digital age”. In addition to Riley, the brief made note of United States v Jones, a 2012 case in which a unanimous court said police needed a warrant to affix a GPS device to a car and monitor its movements: “[N]ovel digital surveillance technologies not in existence at the framing of the Fourth Amendment does not escape the Fourth Amendment’s reach”. Quoting Jones, the petitioners wrote that “[m]onitoring an individual’s location and movements over an extended period of time by collecting and analysing cell phone records can and frequently will expose extraordinarily sensitive details of a person’s life including, potentially, ‘a wealth of detail about . . . familial, political, professional, religious, and sexual associations.’” Given the ubiquity of mobile phones—“95 percent of Americans own a cell phone, and cellular tower coverage spans from coast to coast”—Mr Carpenter’s story is “not an isolated or occasional concern”. In a recent 12-month span, police asked for “staggering volumes” of cell-tower data for their investigations: 75,302 requests for AT&T alone.
The federal government pooh-poohs Mr Carpenter’s claim, pointing to decades of Supreme Court precedents suggesting that since “cell-phone users presumably understand that their phones emit signals that are conveyed to their service providers”, the Fourth Amendment is not threatened when police use cell-site data to build a criminal case. But in agreeing to review Carpenter, the justices may be ready to rethink its own precedents in light of technological advances that were unimaginable in the 1970s when the court was developing its modern Fourth Amendment jurisprudence. As the petitioner points out, in 1986, when the Stored Communications Act was enacted, “cell phones cost over $3,000, were the size of a large brick, could connect to only fragmentary cellular networks and were used by very few people”. Soon we will see whether the justices regard the vast changes in cellular communications over the past three decades—and the powerful new ways in which people can be tracked—as grounds for reconsidering the contours of what Justice Louis Brandeis called “the right to be left alone”.