On June 22, the U.S. Supreme Court ruled that police usually need a search warrant before trying to track a person’s movements using cellphone data, even though the data is in the hands of a third party. In a 5-4 decision in Carpenter v. United States, the court upheld an apparent widening of privacy rights in the digital age.

The Justice Department argued a warrant is not required to access cellphone location information because users voluntarily reveal shared data with their cellular provider. The Supreme Court majority disagreed, saying the realities of modern life make that distinction too simple.

The opinion said that cellphones have become almost a “feature of human anatomy,” and that we “compulsively” carry cellphones with us.

Cellphone Tracking Invades Privacy

Cellphones are carried by users in potentially revealing or compromising locations, so when police track a phone’s location, they effectively achieve a surveillance level akin to the individual wearing an ankle monitor. According to the court, the framers of the Constitution would have understood an individual’s privacy interest in information revealing one’s location on a minute-to-minute basis.

The Supreme Court declined to allow such extensive intrusion based simply on a user’s need to share information with service providers to enable the phone to function.

The ruling held that police must get a warrant in ordinary investigations, but suggested a warrant isn’t required in specific emergency situations. The majority opinion said lower courts could continue to approve warrantless searches in situations like bomb threats, active shootings, and child abductions.

The opinion said the decision did not change legal requirements related to the use of subpoenas to obtain bank, financial, or other business records, nor did it call into question the use of security cameras or “collection techniques involving foreign affairs and national security.” According to the opinion, the decision fulfills the court’s obligation to ensure that scientific developments do not erode the Fourth Amendment’s guarantee of privacy.

In a privacy case a month earlier, the California Supreme Court held that social media companies must provide third-party users’ public content to criminal defendants. 

The social media companies had argued that federal privacy law prevents the release of any user content, and that criminal defendants had ways of accessing the material other than from the company itself. They said criminal defendants could get the information from the individuals themselves or from the prosecutors in the case. 

The defendants involved in Facebook Inc. v. Superior Court of the City and County of San Francisco had sought information from Facebook, Instagram, and Twitter, and wanted videos and other content posted by the victim and a witness. The case was remanded to the trial court for a determination whether the information sought was public or private.