Ever since a little payphone case from 1967, the Supreme Court has been limiting the kind of information law enforcement can get from phones without a warrant. Ever since, courts have struggled to keep up with the changing technology, both in the form of information available from phones, who gathers and shares that information, and the way we use our phones.
Today, the Supreme Court extended the privacy protections for cell phone users, ruling that police must obtain a warrant to get a phone's location information from cell towers.
Data Detection, Collection
The case involved a series of armed robberies of electronics stores in the Detroit area, and the police focused their investigation on Timothy Carpenter, who had allegedly planned the robberies and served as a lookout in a stolen car across the street from the stores. Prosecutors obtained over 127 days' worth of cell phone tower data, tracking his phone to 12,898 locations, including linking his phone to robbery sites. That data was used to convict Carpenter and led to a 116-year prison sentence.
But also contained in that tracking information were Carpenter's whereabouts before and after the robberies, including his sleeping habits and churchgoing schedule. And if police were going to gather that information, according to Chief Justice John Roberts, they needed a warrant. "Mapping a cell phone's location over the course of 127 days provides an all-encompassing record of the holder's whereabouts," Roberts wrote for the 5-4 majority. "As with GPS information, the timestamped data provides an intimate window into a person's life, revealing not only his particular movements, but through them his 'familial, political, professional, religious, and sexual associations.'"
Roberts cited the "seismic shifts in digital technology" that allow wireless carriers to gather "deeply revealing" information about cell phone owners, along with the fact "that carrying one is indispensable to participation in modern society," to demonstrate that cell phone users aren't really sharing information about their location with their carriers voluntarily. Therefore, the Court concluded, the government will generally have to obtain a warrant to acquire cell-site location records.
There may be exceptions to that rule, the Court conceded. Gathering cell-site location records in real time, for a shorter amount of time than in Carpenter's case, in response to emergencies, or getting information about all the phones connected to a particular tower at a particular time may be possible without a warrant. But, for the most part, if police are asking cell phone companies for location data on a particular phone for an extended amount of time, they'll need a warrant.