Senator Ron Wyden (D-Ore.) continues to question various federal agencies about what they know about cell-site simulators, also known as stingrays.

In a new letter submitted Tuesday morning to the head of the Federal Communications Commission, Ajit Pai, Sen. Wyden submitted a slew of new questions concerning how these controversial devices interact with the 911 emergency system. His inquiries come on the heels of efforts last month to scrutinize what the Department of Justice knows about the secretive use of these devices.

In addition, Wyden got a new amendment into an appropriations bill that was approved by the Senate on Monday evening. The amendment requires the Department of Defense to notify the Armed Services Committee about all stingrays detected near military bases during the previous three years and to describe what actions the Department has taken to protect service members and their families against hostile stingrays.

As Ars has reported for years, stingrays determine a phone's location by spoofing a cell tower. In some cases, they can also intercept calls and text messages. Once deployed, the devices intercept data from a target phone along with information from other phones within the vicinity.

Recently, as part of Sen. Wyden's ongoing efforts to shed more light on the shadowy technology, the Department of Homeland Security told the senator that there were foreign-controlled fake cell-tower surveillance devices in Washington, DC. DHS said that not only did it not know how to find them, but the agency could not determine whether stingrays interfere with 911 calls.

Now, Wyden wants to know what the FCC knows about this type of disruption. Among his new questions—which he has said the agency must answer by July 13—he wants to know about what level of testing it has done, and if it hasn’t done testing, why not.

The senator continues:

2. As part of the certification process, does the FCC test whether cell-site simulators might disrupt non-emergency cellular telephone service or wireless Internet access, including both the mobile devices targeted for surveillance and other nearby devices used by innocent bystanders? If so, please describe the findings. If not, why not? 3. What, if any, testing does the FCC conduct or require to assess whether or how cell site simulators affect the functionality of cellular telephone handsets, including any effects on the power consumption and broadcast strength of those handsets? Please provide a detailed explanation of the results of any such testing conducted of cell site simulators certified by the FCC. If the Commission does not conduct or require testing, please explain why the Commission does not believe that such testing is necessary. 4. The FCC is required by law to determine that certification of a device is in the service of the public interest, convenience, and necessity. If an FCC testing certification body determines that a device complies with the technical standards for certification, does the Commission then assume that certification would serve the public interest, convenience, and necessity? If so, why? Please describe how, if at all, the FCC considers the disruption of cellular telephone service, wireless Internet access, or any other applications when deciding if certifying a cell site simulator serves the public interest.

Sen. Wyden is not the only person to be concerned about how stingrays may impact 911 calls.

Nearly two years ago, Laura Moy, a law professor at Georgetown University, filed a formal complaint with the FCC over similar concerns. Nothing seems to have come of her efforts, as far as she can tell.

"These powerful devices can interfere with cellphones that are two blocks or more away," she told Ars. "Stingrays work by hijacking cellphones, turning them into surveillance devices in our pockets and purses. When that happens, affected phones cannot make or receive calls—and that almost certainly includes emergency calls. The FCC should absolutely be doing this testing. Stingrays work by interfering with normal operation of the phone network—that's their core functionality. As regulator and custodian of our communications networks, it's the FCC's job to police that."