Today, the Supreme Court is hearing oral argument in two cases exploring the authority of police to search cellphones taken from people who have been arrested.

The Fourth Amendment protects the right of the people against unreasonable searches and seizures. But “searches” today look quite different from the ones conducted when the Fourth Amendment was adopted. As technology advances, the Supreme Court continually reevaluates the meaning of that term.

For instance, just a few years ago, the Supreme Court determined that the police searched a vehicle when they attached a GPS device to it and monitored its public movements, even though the police would not have searched the vehicle if they just watched it drive by.

Do the police violate the Fourth Amendment by browsing through the contents of an arrestee’s cellphone without first obtaining a search warrant? The Constitution requires police to obtain a warrant from a neutral magistrate supported by probable cause describing what they want to search or seize. As the Supreme Court has explained, the warrant requirement protects the people against “rash and unreasonable interferences with [their] privacy.”

Of course, there are exceptions to the warrant requirement. One exception permits officers to conduct the warrantless search of an arrestee to protect the officer from harm and to preserve evidence. These limited searches, known as a “search incident to arrest,” extend only to the arrestee’s body (e.g., his pockets) and the area within his immediate reach, including containers.

In Riley v. California and United States v. Wurie, the police went further. After the suspects were taken into custody, the police scrolled through text messages and call logs—not to find a weapon or preserve evidence—but to further their investigations. And these weren’t your average flip phones, but more like the digital equivalent of Mr. Riley’s and Mr. Wurie’s homes. Smart phones contain “the kind of information one would previously have stored in one’s home and that would have been off-limits to officers performing a search incident to arrest,” the lower court in Mr. Wurie’s case pointed out. Nevertheless, California and the United States argue that these searches were proper.

In an era when the volume and personal nature of data that people store on their cellphones is significant and likely to grow as technology advances, the Supreme Court will closely consider the ramifications of a decision that will enable police to rummage through cellphones as a matter of course. It may be inconvenient to require police to obtain a warrant before perusing the contents of an arrestee’s cellphone, but the Supreme Court may be willing to err on the side of protecting privacy.