In a major test of how to interpret the Fourth Amendment and privacy rights in the digital age, the Supreme Court heard arguments today about whether the police need warrants to search the cellphones of the people they arrest. The courts have long allowed warrantless searches incident to arrests to protect police officers and to prevent the destruction of evidence. This is the position of the United States Justice Department. The defense takes the position that a different standard must apply because of the sheer amount of personal data on and available on cellphones. The first case that was argued, Riley v. California, No. 13-132, arose out of the arrest of David Riley who was pulled over for having an expired registration. The police found loaded guns in his car and, in his cellphone, they found contacts they associated with a street gang. A more comprehensive search of the phone led to information that linked Riley to a shooting. He was later convicted of attempted murder and sentenced to 15 years to life in prison. The California appeals court held that neither search had required a warrant. The state of California argued that immediate searches are needed because data on cellphones can be erased by remote signal with certain applications. Mr. Riley's lawyers responded that all the police need to do is put the seized phones in airplane mode while they seek a warrant or use Faraday bags, which block remote signals. The second case is United States v. Wurie, No. 12-212, which involved a search of the call log of the cellphone of Brima Wurie who was arrested and charged with gun and drug crimes. The federal appeals court in Boston held that the search violated the defendant's Fourth Amendment rights and must be suppressed.