A woman uses her mobile phone at the plaza of the U.S. Supreme Court in Washington June 25, 2014. The U.S. Supreme Court on Wednesday ruled that police officers usually need a warrant before they can search an arrested suspect's cellphone. The court said on a 9-0 vote in an opinion written by Chief Justice John Roberts that the right of police to search an arrested suspect at the scene without a warrant does not extend in most circumstances to data held on a cellphone. There are some emergency situations in which a warrantless search would be permitted, the court noted.