Once they place a suspect under arrest, police in many parts of this country are allowed to search the contents of his or her mobile phone – including text messages, photos, video files and contacts – without a warrant.

These searches can expose a wealth of personal detail that was inconceivable to the Supreme Court 40 years ago when it gave officers wide latitude to search people and their effects when taking them into custody. It’s time for the court to adapt its doctrine to new technology.

In a case from California, David Riley, a college student, was arrested on a gun charge and police confiscated his smartphone. They found text messages referring to a gang and a photo showing Riley and another man posed near a car that had been involved in a shooting. Riley was convicted in the shooting, after a trial in which prosecutors played a video found on his phone. In seeking review by the Supreme Court, Riley’s lawyers noted that lower courts have been struggling to apply to cellphone searches “a set of legal rules largely developed decades ago, before the digital era.”

Historically, police were allowed to search the possessions of those they arrested because of the possibility that a suspect might threaten the officers with a concealed weapon or might try to destroy evidence.

That threatens a vast invasion of privacy when the object searched isn’t a cigarette pack but a smartphone. The court should make clear that police are not entitled to conduct an electronic fishing expedition into every aspect of a suspect’s life.