In a letter released to the public last week, Senate Judiciary Committee members Patrick Leahy (D-VT) and Chuck Grassley (R-IA) expressed their concerns about the FBI’s defense of the apparently widespread practice of warrantless surveillance of cellular data.

In a private briefing to committee members, the FBI apparently indicated that they do not believe they need warrants in order to secure data from cell technology using decoy towers known as “stingrays.”

“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,” the letter read.

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.

We have concerns about the scope of the exceptions. Specifically, we are concerned about whether the FBI and other law enforcement agencies have adequately considered the privacy interests of other individuals who are not the targets of the interception, but whose information is nevertheless being collected when these devices are being used. We understand that the FBI believes that it can address these interests by maintaining that information for a short period of time and purging the information after it has been collected. But there is a question as to whether this sufficiently safeguards privacy interests.

The congressional investigation was prompted in part by a report published in The Wall Street Journal in November in which the existence of these secret mock cell towers as well as Cessna aircraft that randomly surveil America’s urban centers was revealed.

“The official said discussion of such matters would allow criminal suspects or foreign powers to determine U.S. surveillance capabilities,” The Journal report read. “Justice Department agencies comply with federal law, including by seeking court approval, the official said.”

The Journal report makes it clear that most of the information caught by this form of dragnet surveillance is “let go,” but that appears to be cold comfort to the members of the Senate Judiciary Committee.

Writing in Ars Technica, David Kravets is unimpressed with the FBI’s regard for Americans’ expectation of privacy.

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.

Despite the fleeting outrage that followed revelations that the NSA used the PRISM program to scoop up information on average internet users, little in the way of reforms to the process by which domestic law enforcement agencies collect and use information collected through surveillance on private citizens. Since President Barack Obama has apparently abandoned the pursuit of sweeping reforms to America’s domestic surveillance programs, many will urge his successor to follow up on that unfinished task. It seems, however, that the occupant of the Oval Office’s view of the necessity of these programs differs greatly from that of the public.

Correction: An earlier version of this post claimed that the FBI did not need to seek a a judge’s authority in order to collect information from decoy cell towers.