It sounds like something that James Bond would use: a gadget that self-destructs if it falls into the wrong hands. But it’s actually an open-source operating system that can be downloaded onto Android phones.

Federal prosecutors in Atlanta are bringing an obstruction charge against a U.S. citizen who gave customs officers what is known as a duress passcode, which activated software that erased the contents of his phone.

The authorities stopped Samuel Tunick, an Atlanta resident, for interrogation at Hartsfield-Jackson Atlanta International Airport as he returned to the United States on Jan. 24 last year, according to a November grand jury indictment. The authorities seized his phone before allowing him to enter the country. A hearing on the case was held last week in federal court in Atlanta.

The prosecution is one of the earliest known instances of federal authorities charging a person with destroying evidence with a program designed to wipe a device when a specific code is entered.

Mr. Tunick’s lawyers argued during the hearing last week that the seizure was unlawful, and that he was targeted because of his political activism against Atlanta’s plan to build a police and fire training center within a 1,000-acre stretch of urban woodland. Opponents argue that the center, known as Cop City, would militarize officers and destroy precious green space.

The statute behind the charge

The federal statute underlying the charge makes it a felony to destroy evidence or transfer assets to keep the government from seizing them, or to tip someone off about an upcoming search or wiretap. It carries a penalty of up to five years in federal prison, a fine, or both.

The act applies before, during or after a search. If the target of an investigation knows that a search or seizure is imminent, and that person acts to thwart it, they would fall under the statute, experts said.

Why digital data can be seized

Courts have long treated digital data as property — think about intellectual property theft as one example — so a software wipe is treated in the legal system no differently than flushing physical evidence.

The government’s argument here is that the physical phone was just a container. The data itself was the property that they had lawful authority to seize, and inputting the duress code was the physical act that caused its destruction.

“The statute says explicitly it has to be for the purpose of preventing or impairing the government’s lawful authority,” said Daniel Richman, a law professor at Columbia University and a former prosecutor in the U.S. Attorney’s Office. “The key is he gave the code to the government, knowing that the entry of this code would erase the evidence.”

Does it matter that it was a customs search?

That it was a border search is central to both the government’s prosecution and the defense’s legal challenge.

Customs and border authorities believe that they have the right to search and seize incoming travelers’ digital devices without a search warrant or court order because travelers are not on U.S. soil until they’re authorized to enter.

Mr. Tunick, who was returning from a vacation in the Dominican Republic, and his lawyers argue that even at an international airport, travelers retain vital protections. They said that he was subjected to an unlawful detention, was never read his rights and was repeatedly denied requests to speak with a lawyer.

His lawyers were not immediately available for comment on Tuesday.

How a duress passcode works

A duress passcode is a privacy and security feature in which a user has previously configured a secondary passcode that is not their usual code to unlock the screen. If the user is forced or pressured to hand over their phone, they can provide this passcode instead of the one that unlocks their phone.

When the duress passcode is entered, rather than unlocking the phone, the operating system starts a full wipe of the device’s digital contents. The process leaves the physical device and hardware intact while completely erasing the underlying digital data.

In Mr. Tunick’s case, he used GrapheneOS, a private mobile operating system compatible with some Android phones.

No details on the original investigation

“Many times the government wants to highlight what it was trying to investigate because that ups the stakes on what the defendant was doing,” Professor Richman said. “This is a case where I think they’re trying to avoid exactly that by focusing only on the destruction, and not what the investigation was about.”

The statute that is being used in this case has seldom been cited. It does not require the government to prove or explain the underlying investigation. A statute that is typically used carries a heavier maximum penalty of 20 years, but its use often forces the government to detail their underlying investigation.

“Whether they’ll succeed or not remains to be seen, if this goes to trial,” he said.

The timing matters

Professor Richman suggested that if a traveler decided to delete everything on their phone before going through an airport checkpoint simply because they did not want the government looking at their personal files, they have a strong argument that they did not act with the specific criminal intent to thwart an imminent search.

But there’s a turning point once you are stopped and actively being questioned.

“Intentionally giving a wipe code to people you know to be exercising lawful authority,” he said, “is going to put you squarely in the realm of the statute.”

Kitty Bennett contributed research.