Supreme Court adopts new rules for cellphone tracking

Police generally need a warrant to look at records that reveal where cellphone users have been, the Supreme Court ruled Friday in a big victory for privacy interests in the digital age.

The justices’ 5-4 decision marks a big change in how police may obtain information that phone companies collect from the ubiquitous cellphone towers that allow people to make and receive calls, and transmit data. The information has become an important tool in criminal investigations.

Chief Justice John Roberts, joined by the court’s four liberals, said cellphone location information “is detailed, encyclopedic and effortlessly compiled.” Roberts wrote that “an individual maintains a legitimate expectation of privacy in the record of his physical movements” as they are captured by cellphone towers.

Roberts said the court’s decision is limited to cellphone tracking information and does not affect other business records, including those held by banks. He also wrote that police still can respond to an emergency and obtain records without a warrant.

But the dissenting conservative justices, Anthony Kennedy, Samuel Alito, Clarence Thomas and Neil Gorsuch, cast doubt on Roberts’ claim that the decision was limited. Each wrote a dissenting opinion and Kennedy said in his that the court’s “new and uncharted course will inhibit law enforcement” and “keep defendants and judges guessing for years to come.”

Roberts does not often line up with his liberal colleagues against a unified front of conservative justices, but digital-age privacy cases can cross ideological lines, as when the court unanimously said in 2014 that a warrant is needed before police can search the cellphone of someone they’ve just arrested.

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