Law enforcement officers in Washington, D.C. violated the Fourth Amendment when they used a cell site simulator to locate a suspect without a warrant, a D.C. appeals court ruled on Thursday. The court thus found that the resulting evidence should have been excluded from trial and overturned the defendant’s convictions.

EFF joined the ACLU in filing an amicus brief, arguing that the use of a cell-site simulator without a warrant constituted an illegal search. We applaud the court’s decision in applying long-established Fourth Amendment principles to the digital age.

Cell-site simulators (also known as “IMSI catchers” and “Stingrays”) are devices that emulate cell towers in order to gain information from a caller’s phone, such as locational information. Police have acted with unusual secrecy regarding this technology, including taking extraordinary steps to ensure that use does not appear in court filings and is not released through public records requests. Concerns over the secrecy and privacy have led to multiple lawsuits and legal challenges, as well as legislation.

The new decision in Prince Jones v. U.S. is the latest to find that police are violating our rights when using this sophisticated spying technology without a warrant.

Jones was accused of sexual assault and burglary. Much of the evidence collected against him was derived from cell-site simulators targeting his phone.

The court determined that the use of a cell-site simulator to track and locate Jones was in fact a “search,” despite claims to the contrary from the prosecution. As the court wrote:

The cell-site simulator employed in this case gave the government a powerful person-locating capability that private actors do not have and that, as explained above, the government itself had previously lacked—a capability only superficially analogous to the visual tracking of a suspect. And the simulator's operation involved exploitation of a security flaw in a device that most people now feel obligated to carry with them at all times. Allowing the government to deploy such a powerful tool without judicial oversight would surely “shrink the realm of guaranteed privacy” far below that which “existed when the Fourth Amendment was adopted.” … It would also place an individual in the difficult position either of accepting the risk that at any moment his or her cellphone could be converted into tracking device or of forgoing “necessary use of” the cellphone… We thus conclude that under ordinary circumstances, the use of a cell-site simulator to locate a person through his or her cellphone invades the person's actual, legitimate, and reasonable expectation of privacy in his or her location information and is a search.

The decision should serve as yet another warning to law enforcement that new technologies do not mean investigators can bypass the Constitution. If police want data from our devices, they should come back with a warrant.