The Supreme Court, by a 5-4 vote, ruled that police need a search warrant to obtain location data generated by a cellphone over a period of time. The ruling says that collecting this data from wireless providers without a warrant violates the Fourth Amendment of the U.S. Constitution, which guards against unreasonable search and seizure. Conservative Chief Justice John Roberts joined with the four liberals on the court to write the prevailing decision.
The ruling is limited to cell-site location data. Whether cops need a warrant to see the real time location of a criminal suspect using a cellphone is still undecided. Justice Roberts did note that there are exceptions that would allow authorities to use location data without first getting a warrant. When chasing a suspect, or protecting a person threatened with imminent physical harm, taking the time to request a warrant might not be feasible.
The case behind the ruling dealt with a man named Timothy Carpenter, who had been convicted of robbing multiple Radio Shack and T-Mobile stores in Ohio and Michigan. Law enforcement used past cellphone location data to link Carpenter with the crimes. Carpenter's ACLU attorney said that police needed to have a warrant to get the location data generated by his client's phone to prevent a violation of the Fourth Amendment, and the Supreme Court agreed. Carpenter's bid to suppress the data during trial was denied, and he was convicted of six counts of robbery. Today's ruling is a victory for him.
(The government's argument) "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."-Chief Justice John Roberts, writing for the majority
In three similar cases, the court also ruled against law enforcement. In 2014, the court ruled that with few exceptions, police must obtain a search warrant before going through the content of a cellphone when the user of the device is arrested. Two years before that, the court ruled that a warrant is required before attaching a GPS tracking device to a car.
Today's decision is more restrictive to law enforcement than current federal law is, and could lead to more rulings in the future that protect data produced by smartphones from unauthorized use by the police.