As expected, the Department of Homeland Security (DHS) has released its own stingray requirements. Agents must now obtain a warrant prior to deploying the secretive surveillance tool as part of criminal investigations. This new policy comes over a month after the Department of Justice released its own similarly policy.

The new rules will apply to DHS, as well as agencies that fall under its umbrella, such as the Secret Service, Customs and Border Protection, Immigration and Customs Enforcement.

During a Congressional hearing on stingrays Wednesday, a top DHS official said that the Secret Service uses this as part of its "protective mission"—making sure the president and other dignitaries are not assassinated. That’s believed to be the first time the Secret Service has explicitly acknowledged its use of the devices.

Chris Soghoian, a technologist at the American Civil Liberties Union and a longtime stingray watcher, said on Twitter that he felt vindicated.

I've long suspected that the Secret Service uses Stingrays to protect VIPs. DHS finally confirms it. https://t.co/CDh2YpxBAe — Christopher Soghoian (@csoghoian) October 21, 2015

Like the Department of Justice’s September 2015 stingray requirements, there are also exceptions for both "exigent" and "exceptional circumstances." While the concept of "exigent circumstances" is well-understood in American law, "exceptional circumstances" are not. Many legal experts are baffled as to what exactly the boundaries of the concept are.

In addition, these new DHS rules have no bearing as to how stingrays are used by state and local law enforcement.

However, unlike the corresponding document released by the Department of Justice in September 2015, DHS specifically states that agents must be fully transparent with judges, which historically has not always been the case.

As the DHS policy states:

In all circumstances, candor to the court is of paramount importance. When making any application to a court, DHS law enforcement personnel must disclose appropriately and accurately the underlying purpose and activities for which an order or authorization is sought. Law enforcement personnel must consult with the prosecutors in advance of using a cell-site simulator, and applications for the use of a cell-site simulator must include sufficient information to ensure that the courts are aware that the technology may be used.

In use from coast to coast

The new DHS policy comes after federal agencies, most notably the FBI, have tried to tightly control information about stingrays for years. The FBI and the Harris Corporation, one of the primary manufacturers of the devices, have refused to answer specifics questions from Ars.

Not only can stingrays be used to determine location by spoofing a cell tower, but in some cases they can also be used to 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.

"I'm a lawyer not a technologist, but I will say the DHS—the cell-site simulators that DHS agencies use, both [Homeland Security Investigations] as well as Secret Service are absolutely configured by the vendor to not collect content," Seth Stodder, an assistant DHS secretary, told the House Oversight Committee.

"I could not tell you one way or the other whether they could be, theoretically, configured to collect content but I know for a fact that the cell-site simulators that DHS uses do not collect content and cannot collect content."

Ars has previously reported that while stingrays have been used at the local level for serious violent crimes, they have also been used to investigate ATM robberies, and 911 hangups. In many cases, both federal and local law enforcement have usually been less than transparent about how they are used in court filings.

In 2015, federal authorities have shown a willingness to open up a little about the technology, although the FBI declared in January that it has a right to use the devices in public without a warrant.

Still, as a Wall Street Journal reporter who covered the hearing in person wrote on Wednesday:

JusticeDept official acknowledges they enforce secrecy but not standards on local use of stingrays/dirtboxes — Devlin Barrett (@DevlinBarrett) October 21, 2015

Questions remain

Privacy advocates said that while the DHS policy is a step in the right direction, it is far from a panacea.

"The biggest problem is that it doesn’t always require the government to get a warrant, or delete the data of innocent bystanders swept up in the electronic dragnet," Neema Singh Guliani, an attorney with the American Civil Liberties Union, said in a statement.

"The guidance excludes the protections it does have when DHS uses a stingray outside criminal investigations, like when it monitors protests or patrols border areas, which the government says extends 100 miles into the United States. The guidance also doesn’t apply to state and local agencies that receive money from DHS to buy these devices, which is essential because police are using them more and more."

Sen. Patrick Leahy (D-Vermont), the ranking member on the Senate Judiciary Committee, said in a statement he was equally concerned by the exceptions that DHS believes it has.

"I am disappointed that DHS has included the same problematic exception to the warrant requirement that is in the Justice Department’s policy," he said.

"Additionally, this policy is limited to criminal investigations, and it is not clear what rules will apply to any use of cell-site simulators for other DHS missions. We must ensure stronger protections for the privacy rights of innocent Americans who are not the targets of an investigation."

You can watch the entire three-hour Congressional hearing below.