The US supreme court delivered a landmark endorsement of electronic privacy on Wednesday, ruling that police must obtain a warrant to search the contents of cellphones seized from people they have arrested.

All nine justices joined the ruling on a case hailed by civil liberties campaigners as a crucial test of the rights of individuals to be protected against intrusion into their ever-expanding digital lives.

The opinion of the court, delivered by chief justice John Roberts, recognised that many owners of modern cellphones “keep on their person a digital record of nearly every aspect of their lives”, which may disclose a uniquely large volume of personal information if searched.



"Modern cell phones are not just another technological convenience," Roberts wrote. “With all they contain and all they may reveal, they hold for many Americans the privacies of life.

Reading his ruling from the bench, Roberts went on: “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 justices considered together two separate cases relating to men whose cellphones were searched after their arrests in California and Massachusetts. Both men were convicted of crimes after information recovered from their phones led police to other evidence.

The court sided with arguments put forward in April by lawyers backed by the American Civil Liberties Union and the Electronic Privacy Information Center, who said that these warrantless cellphone searches were not permitted under the fourth amendment of the constitution, which protects Americans from unreasonable searches.

During the hearings in April, the justices considered opposing arguments from government lawyers that police could search digital content from cellphones in the same way they are allowed to handle physical diaries or photographs held by someone at the time of their arrest.



Several questioned at the time why it should be more necessary to obtain a warrant for the search of digital content than for such physical possessions, which may be seized so that officers can prevent the destruction of evidence or check for weapons.



In his opinion, Roberts acknowledged that by barring officers from making warrantless searches, their jobs would be more difficult. “We cannot deny that our decision today will have an impact on the ability of law enforcement to combat crime,” he wrote.

However, in the end the court ruled that “digital data stored on a cell phone cannot itself be used as a weapon to harm an arresting officer or to effectuate the arrestee’s escape. Officers may examine the phone’s physical aspects to ensure that it will not be used as a weapon, but the data on the phone can endanger no one.”



While joining the court’s main ruling, Justice Samuel Alito filed a separate opinion saying that he would prefer Congress and state legislatures to be given leeway to create new rules that would limit the requirement to obtain a warrant in special cases.

Steven Shapiro, the ACLU's national legal director, hailed the decision as "revolutionary" and said that it would "help to protect the privacy rights of all Americans".

"We have entered a new world but, as the court today recognised, our old values still apply and limit the government's ability to rummage through the intimate details of our private lives," Shapiro said in a statement.