FOR all its convenience, the digital age has made privacy an increasingly rare commodity. Search engines are familiar with users' favourite haunts. Internet service providers share individuals' web browsing habits with other companies. And as Timothy Carpenter found out when he was arrested for masterminding a string of armed robberies in 2011, mobile-phone companies have data showing roughly where their owners are at any point in time.
On November 29th, the Supreme Court will consider whether Mr Carpenter’s constitutional rights were violated when authorities obtained several months of mobile-tower data placing him near the scene of the robberies in Michigan and Ohio. Under the Stored Communications Act of 1986, investigators who have “reasonable grounds to believe” that a suspect’s electronic data includes “specific and articulable facts” that are “relevant and material” to their investigation can secure an order compelling providers to hand it over. That’s a far easier bar to reach than reasonable suspicion someone has committed a crime—the threshold for a search warrant. In Carpenter v United States, the justices will ask whether this higher standard, known as “probable cause”, should apply when the government seeks to track our digital footprints.Get our daily newsletter
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The query requires the Supreme Court to revisit the Fourth Amendment’s “right of the people to be secure in their persons, house, papers and effects”. This privacy guarantee, added to the constitution in 1791, safeguards the public against open-ended, “unreasonable” searches and seizures. Mr Carpenter and sixteen amicus (“friend-of-the-court”) briefs argue that access to cell-phone records ought to require a search warrant, while the federal government and four amicus briefs claim, to the contrary, that collecting cell-site data does not qualify as a “search” triggering Fourth Amendment protection.
As they navigate this thicket, the justices have a jumble of prior rulings to guide them. According to the so-called “third-party doctrine”, articulated in two Supreme Court rulings in the 1970s, a person “has no legitimate expectation of privacy in information he voluntarily turns over to third parties” like banks and phone companies. Using this standard, the Sixth Circuit Court of Appeals found that Mr Carpenter’s “expectation of privacy” in his cell-phone location data was “diminish[ed]” by his apparent knowledge that carrying a mobile phone in his pocket makes him a traceable beacon. But Mr Carpenter’s lawyers say the justices should take note of the fact that mobile phones are no longer really optional. “It is essential that people not only own such devices”, his lawyers wrote, “but also that they carry them virtually all the time, wherever they go.” This new reality merits a re-assessment of what falls under the Fourth Amendment umbrella: “The American people have a reasonable expectation that the details of their minute-by-minute travel over time remain private”, Mr Carpenter’s team argues, “as they always have been.” ...