The Ohio Supreme Court said Tuesday police officers must obtain a search warrant before scouring the contents of a suspect's cell phone, unless their safety is in danger.

The American Civil Liberties Union of Ohio described the ruling as a landmark case. The issue appears never to have reached another state high court or the U.S. Supreme Court.

The Ohio high court ruled 5-4 in favor of Antwaun Smith, who was arrested on drug charges after he answered a cell phone call from a crack cocaine user acting as a police informant.

Officers took Smith's cell phone when he was arrested and, acting without a warrant and without his consent, searched it. They found a call history and stored numbers that showed Smith had previously been in contact with the drug user.

Smith was charged with cocaine possession, cocaine trafficking, tampering with evidence and two counts of possession of criminal tools.

During his trial, Smith argued that the evidence obtained through the cell phone search was inadmissible because it violated the constitutional ban on unreasonable search and seizure.