On June 22, the U.S. Supreme Court decided that the police need a search warrant if they want to track criminal suspects’ movements through cellphone location data. The justices’ 5-4 ruling is considered a win for privacy in the digital age.
The outcome of the case, Carpenter v. United States, marks a significant change in how law enforcement can gain access to phone records. Before the ruling, authorities can go to a phone company and obtain information about the numbers dialed from a cellphone without providing a search warrant.
Chief Justice John Roberts wrote the majority opinion, which was joined by the court’s four liberal justices. Most recently, the court ruled that law enforcement cannot use GPS tracking equipment to track vehicles or search cellphones without a warrant.
The case stemmed from a string of armed robberies of Radio Shack and T-Mobile stores in Michigan and Ohio in 2010 and 2011. In order to prosecute its case against Timothy Carpenter, the government obtained cellphone records that disclosed his approximate location over 127 days, placing him in proximity to four of the criminal offenses.
Lower courts upheld the search of cell tower records according to the “third-party doctrine,” used in previous Supreme Court cases to justify government access to suspects’ bank account records and telephone numbers called from landlines. However, the court ruled that cellphone location data is different, considering it a Fourth Amendment search.
“The government's position fails to contend with the seismic shifts in digital technology that made possible the tracking of not only Carpenter's location but also everyone else's, not for a short period but for years and years,” Roberts wrote.
He said allowing government access to historical GPS data infringes on Carpenter’s Fourth Amendment protections and expectation of privacy, by providing the police with an “all-encompassing record” of his whereabouts. Roberts added that historical GPS data offers an “even greater privacy risk” compared to real-time GPS monitoring.
However, the chief justice said conventional surveillance techniques and tools, including security cameras or real-time cellphone location data monitoring, remain constitutional. Additionally, warrants are not necessary in extreme cases involving imminent threats.