The District of Columbia Court of Appeals ruled that the warrantless use of a cell-site simulator violated the Constitution when a man suspected of sexual assault and robbery was located by local police.

In a 2-1 opinion issued Thursday, the DC Court of Appeals—effectively the equivalent of a state supreme court—agreed with the lower court's ruling that the use of the device, also known as a stingray, was unconstitutional. In addition, however, the judges went further: they found that the violation was so egregious that any evidence derived from the stingray should be excluded from the case, which overturned the conviction.

The case, Prince Jones v. United States, joins a recent string of judgements from around the country that concluded that stingrays are a "search" under the Fourth Amendment. That means they require a warrant, barring exigent circumstances or other known exceptions.

"A person's awareness that the government can locate and track him or her using his or her cellphone likewise should not be sufficient to negate the person's otherwise legitimate expectation of privacy," the majority concluded in the Thursday ruling.

As Ars has long reported, stingrays can be used to determine a mobile phone's location by spoofing a cell tower. In some cases, stingrays can also intercept calls and text messages. Once deployed, the devices intercept data from a target phone along with information from other phones within the vicinity. At times, police have falsely claimed the use of a confidential informant when they have actually deployed these particularly sweeping and intrusive surveillance tools.

Last month, a federal judge in Oakland, California, reached the same conclusion as the DC court. However, in that case, US v. Ellis, US District Judge Phyllis Hamilton found that there was exigency, which is the notion in American criminal procedure that law enforcement can search or seize persons or things if there are imminent circumstances where bodily harm or injury is in process, evidence is being destroyed, or a suspect is in flight. In such situations, warrants aren’t required.

In July 2016, a federal judge in New York ruled along similar lines as the DC Court of Appeals in a case known as United States v. Lambis.

"Absent a search warrant, the Government may not turn a citizen's cell phone into a tracking device," US District Judge William Pauley wrote in that case.

ACLU attorney Nate Wessler, who argued as an amicus (friend of the court) on behalf of Jones, applauded the ruling. In a statement e-mailed to Ars, he wrote: