The U.S. Supreme Court will hear arguments today in a pair of major Fourth Amendment cases testing the reach of police powers. At issue in both Riley v. California and United States v. Wurie is whether law enforcement must obtain a warrant before conducting a cellphone search incident to arrest. As I explained in a recent column, the Court's answer to that question is likely to have a profound impact on the rights of all Americans in their dealings with the police:

According to a long line of Supreme Court precedent, the police do not need a warrant to search the individuals they arrest, and that includes both the persons and possessions of the arrestees, including any bags, containers, or other items they were carrying. Furthermore, the police may conduct a warrantless search of the immediate vicinity around the arrest site. This exception is designed to help law enforcement prevent the destruction of evidence and to discover any evidence or weapons that might have been concealed.

The rise of the cellphone complicates this picture. Unlike diaries, notebooks, or briefcases, all of which the police are allowed to search incident to arrest, cellphones contain previously unimaginable amounts of personal information, including not only words and images but also GPS location data. In other words, should getting arrested for a minor offense like jaywalking be sufficient to allow the police virtually unlimited access to your private affairs in search of additional wrongdoing?

These cases go to the very heart of the Fourth Amendment, which not only protects "the right of the people" to be free from "unreasonable searches and seizures;" it requires the government to show "probable cause" and describe "the place to be searched, and the person or things to be seized" before a warrant will be issued. That language was added to the Constitution in order to repudiate the colonial era practice of issuing "general warrants," those notorious blank checks cited by snooping British officials. It takes no leap of imagination to see a warrantless cellphone search—which gives today's police snoops a window into every nook and cranny of one's private life—as the modern day equivalent of the justly banished "general warrant."

We'll find out soon which way the Supreme Court sees it.