Do the police need a warrant to search your cell phone?
The general rule is that a warrantless search is only reasonable if it falls under a specific exception to the Fourth Amendment warrant requirement. See Kentucky v. King.
One exception to the warrant requirement is a search conducted incident to arrest. See Chimel v. California.The basic premise of this exception is that warrantless searches are generally allowed at the time an individual is arrested. However, law enforcement is typically permitted to search only those items within the wingspan or reach of the arrested party. Furthermore, the search is only to ensure officer safety and prevent the destruction of evidence.
Prior to Chimel v. California, law enforcement was using this exception to the warrant requirement in order to search cell phones incident to arrest. The United States Supreme Court recently heard a case involving these very facts and was tasked with deciding if the search of a cell phone should be allowed during an arrest.
The court held that, in general, a warrant is needed to search a cell phone and does not fall under the search incident to arrest doctrine. The court concluded that the information on a cell phone is not immune from search, but rather that a warrant is required to do so. See Riley v. California.
Therefore, absent providing consent, search of a cell phone generally necessitates a warrant.