In Riley v. California, the United States Supreme Court unanimously held that the Fourth Amendment prohibits police officers from searching through the data on an arrested suspect's cell phone as an "incident to the arrest" and instead ruled that police officers must get a warrant first.

Riley involved the facts of two separate cases. In the first case, officers searched through the smartphone of a suspect arrested for expired registration and possession of illegal firearms and found photos and text messages showing that the arrestee was involved in a gang shooting a few weeks earlier. In the second case, officers arrested a suspect after observing him complete a drug deal, searched his traditional cell phone (not a smart phone) for the phone number associated with his home, traced the number to his house, and found a large amount of drugs and cash, along with a firearm and ammunition. In both cases, the evidence obtained through the warrantless cell phone searches was admitted at trial and both defendants were convicted.

The Court's analysis focused on the reach of a warrantless search "incident to a lawful arrest." Under this exception, police officers are permitted to search the person arrested and the area within their immediate control to remove any weapons that may be used to resist arrest or endanger the officers and to prevent the destruction of evidence. See Chimel v. California, 395 U.S. 752 (1969). The Court took the time to appreciate the complexity of modern cellphones, describing them as "minicomputers that also happen to have the capacity to be used as a telephone" that are "a pervasive and insistent part of daily life." The Court then analyzed the two justifications in Chimel for allowing a search incident to arrest: officer safety and destruction of evidence. With respect to officer safety, the Court concluded that data cannot harm officers and examples of cellphones indirectly contributing to unsafe arrest scenes were insufficient to dispose of the warrant requirement. With respect to the destruction of evidence, the Court found that examples of remote data-wiping of cellphones in police custody were rare and could be prevented by removing the battery or storing the phone in a bag designed to block wireless signals.

As further justification, the Court examined the privacy issues that arise from allowing warrantless searches of cellphones incident to arrest. Because modern cellphones carry the equivalent of "cameras, video players, rolodexes, calendars, tape recorders, libraries, diaries, albums, televisions, maps, or newspapers" in a person's pocket, the Court found that searches incident to arrest were not "limited by physical realities" of what a person can carry. Thus, allowing warrantless searches incident to arrest could reveal "far more than the most exhaustive search of a house." The Court also noted that the scope of data that can be reached by cellphones, such as information uploaded to cloud servers, necessitated a warrant requirement and the proposed solutions to allow but limit warrantless searches were unworkable. Finding that cellphones store "the privacies of life," the Court held that police must do one simple thing before searching a cell phone seized incident to an arrest: "get a warrant."

For a full copy of the opinion, click here.