In its 2014 decision in Riley v. California, the U.S. Supreme Court held that law enforcement officials violated the Fourth Amendment when they searched an arrestee's cell phone without a warrant. "Modern cell phones are not just another technological convenience," Chief Justice John Roberts wrote for the majority. "With all they contain and all they may reveal, they hold for many Americans 'the privacies of life.' The fact that technology now allows an individual to carry such information in his hand does not make the information any less worthy of the protection for which the Founders fought."

But what about when an American citizen is returning home from abroad and U.S. border officials want to thoroughly search the contents of that person's cell phone? Does the Fourth Amendment require the government to get a warrant before searching cell phones at the border? According to a decision issued this week by the U.S. Court of Appeals for the 11th Circuit, the answer to that question is no.

The 11th Circuit's ruling came in the matter of United States v. Vergara. Hernando Vergara is a U.S. citizen who was returning home from a cruise to Mexico. Because of a prior conviction for possessing child pornography, a Customs and Border Protection officer searched his luggage, including the three cell phones that Vergara was carrying. One of those phones contained "a video of two topless female minors." The Department of Homeland Security entered the picture at that point. Vergara's cell phones were taken away to a DHS facility where they were subjected to a warrantless forensic search, which typically involves retrieving deleted files and other significant inspections of the phone's digital records. DHS discovered child pornography on Vergara's phones.

Vergara and his lawyers argue that this evidence should be deemed inadmissible because the government never obtained a search warrant. His position is based in significant part on the increased privacy protections for cell phone users that the Supreme Court recognized in Riley v. California.

But a divided panel of the 11th Circuit took a different view. "The forensic searches of Vergara's cell phones occurred at the border, not as searches incident to arrest," declared the majority opinion of Judge William H. Pryor. "And border searches never require a warrant or probable cause."

Writing in dissent, Judge Jill Pryor wrote that while she agrees "with the majority that the government's interest in protecting the nation is at its peak at the border," she disagrees "with the majority's dismissal of the significant privacy interests implicated in cell phone searches." In Riley, she noted, the Supreme Court recognized "the significant privacy interests that individuals hold in the contents of their cell phones." And in her view, "the privacy interests implicated in forensic searches are even greater than those involved in the manual searches at issue in Riley." If it were up to her, "a forensic search of a cell phone at the border [should require] a warrant supported by probable cause."

One thing is clear: We have not heard the last of this debate. Either this case, or one very much like it, is almost certainly headed for the Supreme Court.