Today the U.S. Supreme Court held that the Fourth Amendment requires police to obtain a warrant before searching the digital contents of cell phones taken from people who have been arrested.

The Fourth Amendment protects the right of the people against unreasonable searches and seizures. The Constitution generally requires police to obtain a warrant from a neutral magistrate supported by probable cause describing with particularity what they want to search. There are exceptions to this requirement, but the Court declined to broaden the search-incident-to-arrest exception today. Under this exception, officers may conduct warrantless searches of an arrestee to protect the officer from harm and to preserve evidence. These limited searches extend only to the arrestee’s body (e.g., his pockets) and the area within his immediate reach, including containers.

As the Court recognized, “searches” today look quite different from the ones conducted when the Fourth Amendment was adopted. Starting from the premise that cell phones have become “such a pervasive and insistent part of daily life that the proverbial visitor from Mars might conclude they were an important feature of human anatomy,” the Court concluded that the search-incident-to-arrest exception does not apply to cell phone searches. Lumping together the search of an arrestee’s pocket’s with a search of his cell phone, the Court reasoned, “is like saying that a ride on horseback is materially indistinguishable from a flight to the moon.”

The Court acknowledged that there may be some circumstances when the warrantless search of a cell phone is justified under another of the established exceptions to the warrant requirement. But given the privacy interests at stake, the Court was unwilling to allow police unfettered access to cell phones. Indeed, searching a cell phone is more like finding a key in a suspect’s pocket and using it to search his home, an action that clearly requires a warrant.

In concluding, the Court noted:

“The fact that technology now allows an individual to carry such information in his hand does not make the information any less worthy of the protection for which the Founders fought. Our answer to the question of what police must do before searching a cell phone seized incident to an arrest is accordingly simple—get a warrant.”