In 2014, the Supreme Court unanimously ruled in Riley v. California that police can't search a cell phone without a warrant during an arrest -- and explicitly said the plain view doctrine doesn't apply to digital data. Chief Justice Roberts wrote the opinion, noting that a phone's data "can endanger no one" once the device is physically secured.
The plain view doctrine lets police seize evidence without a warrant when three conditions are met, as the Court established in Horton v. California (1990): the officer is lawfully present, has legal access to the object, and the item's criminal nature is "immediately apparent." If a cop executing a drug warrant spots a stolen television in the living room, they can seize it on the spot. But the doctrine has limits -- in Arizona v. Hicks (1987), the Court ruled that moving a stereo to check its serial number went beyond plain view and required probable cause. The Riley decision drew a hard line at digital devices, recognizing that a smartphone holds more private information than a home. As courts confront questions about laptop screens, smart home cameras, and wearable devices, the boundary between what officers can see and what they can search keeps shifting.