A federal judge has struck a blow for privacy, ruling that authorities must obtain a warrant before searching cell phones at the border.

The US border has been a legal gray area for years — a zone where the Fourth Amendment doesn’t fully apply — with authorities able to search people’s cell phones, computers, luggage, and other possessions without a warrant.

According to the Electronic Frontier Foundation (EFF), a New York district judge has become the first to rule that cell phone searches at the border require a search warrant:

With United States v. Smith (S.D.N.Y. May 11, 2023), a district court judge in New York made history by being the first court to rule that a warrant is required for a cell phone search at the border, “absent exigent circumstances” (although other district courts have wanted to do so).

The judge in the case relied heavily on the precedent set in the Riley vs California (2014) case, in which the Supreme Court ruled that police need a warrant to search the cell phone of someone they have arrested.

As the EFF explains, much of the Supreme Court’s decision in the Riley case balanced the need for police to search a suspect against the immediate threat posed.

In Riley, the Supreme Court applied a balancing test, weighing the government’s interests in warrantless and suspicionless access to cell phone data following an arrest, against an arrestee’s privacy interests in the depth and breadth of personal information stored on modern cell phones.

In analyzing the government’s interests, the Riley Court considered the traditional reasons for authorizing warrantless searches of an arrestee’s person: to protect officers from an arrestee who might use a weapon against them, and to prevent the destruction of evidence.

The Riley Court found only a weak nexus between digital data and these traditional reasons for warrantless searches of arrestees. The Court reasoned that “data on the phone can endanger no one,” and the probability is small that associates of the arrestee will remotely delete digital data.

The judge in the New York case applied that same reasoning to warrantless border searches.

Just as in Riley, the cell phone likely contains huge quantities of highly sensitive information—including copies of that person’s past communications, records of their physical movements, potential transaction histories, Internet browsing histories, medical details, and more … No traveler would reasonably expect to forfeit privacy interests in all this simply by carrying a cell phone when returning home from an international trip.

The decision is good news for travelers who don’t want to surrender their privacy without good cause.