In the case of Riley versus California, the United States Supreme Court ruled that the police generally may not, without a warrant, search the contents of a cell phone that is taken from someone who has been arrested. The facts in the Riley case are as follows:
David Riley was stopped for a traffic violation which eventually led to his arrest on weapons charges. While searching Riley, a police officer found a cell phone located in his pants pocket. The officer looked at information contained on the phone and noticed the repeated use of a term associated with a street gang. A few hours later, a detective at the police department who specialized in gangs further examined information contained on Riley's phone. Based in part on photographs and videos that the detective found, the prosecutor's office charged Riley in connection with a shooting that had occurred a few weeks earlier and sought an enhanced sentence based upon his gang membership.
Riley filed a motion in which he argued that it was illegal for the police to have searched the contents of his phone without first getting a search warrant. The United States Supreme Court agreed with him. The Court said that when the police arrest someone, they are allowed to search items found on his person without first getting a warrant if those items can harm an officer or be used to escape (for example, a gun) or if those items can be destroyed (for example, drugs). However, in the case of cell phones, data stored on a phone cannot be used as a weapon to harm an officer or to help someone escape from the police. Also, the Supreme Court rejected the argument that the police should not be required to get a search warrant because evidence on a cell phone can be destroyed by remote wiping and data encryption. The Court said that neither of those things is all that prevalent in our society.
The Supreme Court was also concerned about the privacy interests that are at stake when cell phone data is involved. Cell phones can store millions of pages of text, thousands of pictures, and hundreds of videos. Thus, a cell phone can contain an electronic record of nearly every aspect of someone's life. And because of those privacy concerns, the police are required to get a search warrant before looking at the contents of someone's cell phone whom they have recently arrested.