Following revised policies from other federal law enforcement agencies, the Internal Revenue Service now says it will require the use of a warrant when deploying a stingray, also known as a cell-site simulator.

In a new letter to an Oregon senator, IRS Director John Koskinen wrote that the stingray has only been used as part of 11 grand jury investigations to track 37 phones. The IRS stingray has also been used to assist with four other non-IRS investigations both at the federal and the state level. According to the document, the IRS first obtained its stingray in October 2011, and it's attempting to procure a second.

Stingrays, also known as cell-site simulators, can be used to determine a phone’s location by spoofing a cell tower, and in some cases they can intercept calls and text messages. Once deployed, the devices intercept data from a target phone as well as information from other phones within the vicinity. In late October, Koskinen told a Senate committee that the IRS stingrays are "only used in criminal investigations."

The director's new remarks come just one day after The Guardian revealed that the IRS had made two purchases from well-known surveillance device manufacturer Harris Corporation in 2009 and 2012. Previously during a hearing, Sen. Ron Wyden (D-Ore.) had asked Koskinen to provide the number of times that its stingray had been used. Koskinen then promised to do it in writing.

In addition to the warrant promise, Koskinen elaborated on the new IRS policy in his letter to Wyden: