The Fourth Amendment protects our "persons, houses, papers, and effects, against unreasonable searches and seizures." That includes the cell phones in our pockets, and the many private messages, photos, and videos those devices contain. But what happens if we get arrested for a minor (or major) infraction? Do the police now have the lawful right to search our cell phones for incriminating material without a warrant? Or does the Constitution still act as a shield?

The U.S. Supreme Court will address those questions next month when it considers a pair of cases testing the reach of the Fourth Amendment in the age of the smartphone. The Court's response has the potential to impact the lives of countless of Americans in their dealings with the police.

Both cases began with criminal arrests. In the first case, Riley v. California, San Diego police conducted a routine traffic stop and discovered two guns hidden under the hood of the car. After bringing the suspect back to the station, the officers proceeded to conduct a warrantless search of his smartphone, where they discovered videos, photos, and text messages they believed tied him to a gang-related shooting. That evidence later helped the prosecution gain a conviction.

In the second case, United States v. Wurie, Boston police arrested a suspected drug dealer. Back at the station, they noticed his flip-screen cell phone was receiving multiple calls from a number identified on the outer screen as "my house." According to the officers, they suspected this might in fact be the dealer's "stash house," so they traced the number back to an address, and later raided the residence, turning up illegal drugs. In both cases, the officers had ample time to obtain a search warrant before digging around in the respective cell phones.

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 cell phone complicates this picture. Unlike diaries, notebooks, or briefcases, all of which the police are allowed to search incident to arrest, cell phones 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?

The lower courts are divided. In 2013, the California Supreme Court ruled against David Riley, letting the warrantless search of his cell phone stand. The U.S. Court of Appeals for the 1st Circuit, by contrast, ruled against the police that same year in the Boston case, adopting a "bright-line rule" that "the search-incident-to-arrest exception does not authorize the warrantless search of data on a cell phone seized from an arrestee's person" under any circumstances.

The Obama administration has sided with the police. "Although cell phones can contain a great deal of personal information," the administration argues in its Wurie brief, "so can many other items that officers have long had authority to search, and the search of a cell phone is no more intrusive than other actions that the police may take once a person has been lawfully arrested."

The lawyers representing David Riley take the opposite view, comparing a warrantless cell phone search incident to arrest to the "odious colonial-era practice of executing general warrants—warrants that enabled officers to rummage though people's homes and offices for whatever incriminating items they might find."

An amicus brief filed by a group of Fourth Amendment scholars urges the justices to strike a balance. "Rather than allowing warrantless searches of cell phones incident to arrest," the brief argues, "the Court should encourage law enforcement officers to place cell phones in [aluminum-lined] Faraday envelopes or aluminum foil to prevent the remote wiping of data from the phone while officers seek a warrant." This approach has the virtue of allaying any law enforcement concerns about the destruction of evidence while still respecting the citizenry's constitutional rights.

Oral arguments in Riley v. California and U.S. v. Wurie are scheduled for April 29, 2014.