The Federal Bureau of Investigation is taking the position that court warrants are not required when deploying cell-site simulators in public places. Nicknamed "stingrays," the devices are decoy cell towers that capture locations and identities of mobile phone users and can intercept calls and texts.

The FBI made its position known during private briefings with staff members of Senate Judiciary Committee Chairman Patrick Leahy (D-Vt.) and Sen. Chuck Grassley (R-Iowa). In response, the two lawmakers wrote Attorney General Eric Holder and Homeland Security chief Jeh Johnson, maintaining they were "concerned about whether the FBI and other law enforcement agencies have adequately considered the privacy interests" of Americans.

According to the letter, which was released last week:

For example, we understand that the FBI’s new policy requires FBI agents to obtain a search warrant whenever a cell-site simulator is used as part of a FBI investigation or operation, unless one of several exceptions apply, including (among others): (1) cases that pose an imminent danger to public safety, (2) cases that involve a fugitive, or (3) cases in which the technology is used in public places or other locations at which the FBI deems there is no reasonable expectation of privacy.

The letter was prompted in part by a Wall Street Journal report in November that said the Justice Department was deploying small airplanes equipped with cell-site simulators that enabled "investigators to scoop data from tens of thousands of cellphones in a single flight, collecting their identifying information and general location."

The bureau's position on Americans' privacy isn't surprising. The Obama Administration has repeatedly maintained that the public has no privacy in public places. It began making that argument as early as 2010, when it told a federal appeals court that the authorities should be allowed to affix GPS devices on vehicles and track a suspect's every move without court authorization. The Supreme Court, however, eventually ruled that warrants are required. What's more, the administration has argued that placing a webcam with pan-and-zoom capabilities on a utility pole to spy on a suspect at his or her residence was no different from a police officer's observation from the public right-of-way. A federal judge last month disagreed with the government's position, tossing evidence gathered by the webcam that was operated from afar.

In their letter, Leahy and Grassley complained that little is known about how stingrays, also known as ISMI catchers, are used by law enforcement agencies. The Harris Corp., a maker of the devices from Florida, includes non-disclosure clauses with buyers. Baltimore authorities cited a non-disclosure agreement to a judge in November as their grounds for refusing to say how they tracked a suspect's mobile phone. They eventually dropped charges rather than disclose their techniques. Further, sometimes the authorities simply lie to judges about their use or undertake other underhanded methods to prevent the public from knowing that the cell-site simulators are being used.

"The Judiciary Committee needs a broader understanding of the full range of law enforcement agencies that use this technology, the policies in place to protect the privacy interests of those whose information might be collected using these devices, and the legal process that DOJ and DHS entities seek prior to using them," Leahy and Grassley wrote in their letter to Holder and Johnson.

Hanni Fakhoury, an attorney for the Electronic Frontier Foundation, said some states and judges are pushing back against stingrays.

"In Tacoma, judges now require police (to) specifically note they plan to use an IMSI catcher and promise not to store data collected from people who are not investigation targets," he said. "The Florida and Massachusetts state supreme courts ruled warrants were necessary for real-time cell phone tracking. Nine states—Colorado, Illinois, Indiana, Maryland, Minnesota, Tennessee, Utah, Virginia, and Wisconsin—passed laws specifically requiring police to use a warrant to track a cell phone in real time."