Police departments in 18 states have deployed a technology called "Stingray" to track individual cell phones in the local war on terror. But its being used for drug crimes and other non-terrorism investigations, and police departments say they aren't allowed to talk about it.

The technology essentially tricks individual cell phones into thinking that it’s a cell phone tower, giving police the ability to scour large areas for an individual cell phone’s “ping” signal. A new disclosure from the FBI revealed this week that state and local police departments are sworn to secrecy before they're allowed to use it.

This week the FBI, complying with a Freedom of Information Act request, revealed a letter from the bureau to a police chief in Tacoma, Washington, stating that the Federal Communications Commission authorizes the sale of Stingray equipment only if municipal departments agree to sign an FBI “non-disclosure agreement.”

The letter was dated Dec. 19, 2012, but first published Monday by MuckRock.com. Four of the document’s six pages were redacted entirely, although the two paragraphs that have been made public are enough to reveal that the FBI is involved with facilitating the “acquisition of certain wireless collection equipment/technology manufactured by Harris Corporation.” 

High levels of secrecy and rumors about the Stingray’s power, though, have contributed to a lingering curiosity about the surveillance technology. Known throughout the law enforcement community as an International Mobile Subscriber Identity catcher, the Stingray is a suitcase-sized metal box that’s typically transported in the back of police vehicles. Harris Corp. charges as much as $400,000 for each device, with the federal government footing the bill for local police departments who say they should be given a Stingray to investigate potential terrorists in their area.

What actually happens, though, tends to be quite different. In 2008 the Tallahassee, Florida, Police Department was investigating an assault and rape in which the victim had her phone stolen. Using the phone’s unique IMSI number (obtained from Verizon), the police drove through the general area where the theft had taken place, deploying the Stingray to search for that IMSI number amid the thousands of other cell phones in the area.

In the process of searching for that individual IMSI number, the TPD could have obtained location data from every phone that connected to the Stingray, all the numbers dialed by a connected phone including outgoing calls and text messages, and identification/telephone numbers for each connected phone, including information they could use to obtain historical phone data and the owner’s payment information.

The tracking software was precise enough to figure out where in an apartment building the woman’s stolen phone was located.

“Using portable equipment, we were able to actually basically stand at every door and every window in that [area] and determine, with relative certainty you know, the particular area of the apartment that that handset was emanating from,” TPD investigator Chris Corbitt explained while testifying on the matter, as quoted in court documents obtained by the ACLU.

At least 43 police agencies in 18 states have Stingrays, using them for a variety of criminal investigations ranging from drugs to violent offenses, with a police spokesman in Georgia saying in July that it’s used “in criminal investigations with no restrictions on the type of crime.” Before that, the ACLU said, the U.S. Marshals Service conspired with local police in Florida to mislead a judge about the Stingray’s technical capabilities.

Hanni Fakhoury, an attorney at the Electronic Frontier Foundation whose specializes in privacy and criminal law, recommended that the dozens of police departments using Stingrays simply announce to the public what it is, what they’re doing with it and how it will help the community.

“I think the public is willing to accept that these devices are useful in solving crimes,” he said. “The obfuscation undermines the government’s use of this technology. Part of the reason we have a search warrant requirement is to make sure there’s a judge there to oversee police and make sure they don’t overstep their bounds.”

Last month the FCC launched an investigation into potential criminal use of IMSI catchers after Rep. Alan Grayson, D-Fla., suggested they could be used by criminals or spies hidden within the U.S. And privacy advocates have called on the government to keep an eye on police departments that they say are violating the Fourth Amendment’s protection against unreasonable search and seizure.

“I think what scares citizens the most is either the intentional or unintentional statements about this technology made by the authorities,” said Barry Covert, a Buffalo, New York, attorney who criticized the local police for relying on Stingrays for everyday investigations. “Now people who are not the target of these investigations have been compromised, and we’re relying on the discretion of the law enforcement agency without any judicial approval or supervision. The Fourth Amendment doesn’t say you can take all this information and comb through it later.”

Along with challenges from the ACLU and EFF, though, there’s growing talk that legal challenges will bring the Stingray debate into open court. Fakhoury expects that the issue will be resolved soon, with growing media attention and judicial questions increasing the pressure on law enforcement.

“We still need to find out how these things are used,” he said. “We’re going get this information. You can’t hide this thing forever, especially now that the cat’s out of the bag.”