In a 5-4 decision, the U.S. Supreme Court gave a victory to privacy advocates Friday, ruling that police generally must have permission from a judge before they can get cell phone records to plot the movements of individual customers.
The decision requires police departments nationwide to get a search warrant in order to obtain telephone company data to track where a user has been. The technique is widespread, given that 95 percent of Americans own a cell phone.
Chief Justice John Roberts, who wrote the court’s opinion, said “a phone goes wherever its owner goes, conveying to the wireless carrier not just dialed digits, but a detailed and comprehensive record of the person’s movements.”
Roberts was joined by the court’s four liberals, justices Ruth Bader Ginsburg, Stephen Breyer, Sonia Sotomayor and Elena Kagan. Justice Anthony Kennedy and the court’s other conservatives dissented.
When used for calls or text messages, a cell phone signals a nearby antenna tower to connect with the telephone network. As the user travels, the call is handed off to successive towers, and the cell phone companies keep records of the phone numbers routed through each tower to sort out such things as roaming charges.
By mapping which towers were used by a given phone number, police can reconstruct a person’s whereabouts over days, weeks, or months.
Friday’s ruling said police can still get cell phone records without a warrant in such emergencies as “the need to pursue a fleeing suspect, protect individuals who are threatened with imminent harm, or prevent the imminent destruction of evidence.”
The Supreme Court’s ruling came in a case brought by a Michigan man, Timothy Carpenter, who was convicted of robbing a string of Radio Shack and T-Mobile stores after FBI agents used three months of cell phone records to show that he was near each store at the time of the crimes. He argued that because the FBI did not get a search warrant, that evidence, along with his conviction, should be thrown out.
Carpenter lost in the lower courts, which ruled that no search warrant was needed because phone customers have no expectation that their records will be private. Those decisions relied on a Supreme Court case from 38 years ago. It said phone customers don’t expect that the numbers they dial will remain private, because the phone company uses that information for billing.