In a story straight out of Spy vs Spy, unusual cellular activity has been detected around Capitol Hill, and now four U.S. Senators want some answers.

A bipartisan group of senators sent a letter to Homeland Security asking for details about the cellular activity. The surveillance activity is akin to so-called stingrays that are used by law enforcement agencies to trick suspects’ cellphones into revealing their locations, according to Reuters.

Last month, the Department of Homeland Security revealed that it had “observed anomalous activity in the National Capital Region that appears to be consistent with International Mobile Subscriber Identity catchers.” It claimed not to know who was behind the use of the surveillance devices.

In the letter, the senators asked the Trump administration to release details about the possible surveillance. “The American people have a legitimate interest in understanding the extent to which U.S. telephone networks are vulnerable to surveillance and are being actively exploited by hostile actors,” the senators wrote in the letter reviewed by Reuters.

Stingray devices mimic cellphone towers in order to force cellphones in the area to transmit “pings” back to the devices, enabling law enforcement to track a suspect’s phone and pinpoint its location. FCC Commissioner Jessica Rosenworcel said at a commission meeting on Tuesday that the issue was serious and surveillance tools could potentially be in use “by foreign or criminal actors.” Or, you know, the show-runners for Homeland.