The US Supreme Court issued a key ruling in favor of Fourth Amendment rights in the digital age June 25, finding unanimously that police in most cases need a warrant before searching the cell phone or personal electronic device of an arrestee. Chief Justice John Roberts firmly rejected arguments that searches of digital devices are comparable to searches police routinely carry out for contraband after making an arrest. In the cases of Riley v. California and United States v. Wurie (argued separately, but decided together), Roberts wrote: "Modern cell phones, as a category, implicate privacy concerns far beyond those implicated by the search of a cigarette pack, a wallet, or a purse... 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."

The court did find that while the police may not search the cell phone data, they may search the phone itself to make sure it cannot be used as a weapon. Justice Samuel Alito filed a concurring opinion, agreeing with the court's basic holding on warrants but saying he'd give legislatures greater leeway to set rules limiting the warrant requirement in certain circumstances. The Justice Department issued a statement pleding to work with law enforcement to assure "full compliance" with the ruling.

The decision comes days after an appeals court ruling in Atlanta similarly found for the Fourth Amendment on the related quesiton of whether police need a warrant to get a person's cell phone location history from the service provider.