"It's not technically hard to make a device that complies with the FCC that listens to nonpublic bands but then is quietly waiting for some activation trigger to listen to other bands," said Eduardo Rojas, who leads the radio spectrum lab at Embry-Riddle Aeronautical University in Florida. "Technically, it's feasible."

To prove a device had clandestine capabilities, Rojas said, would require technical experts to strip down a device "to the semi-conductor level" and "reverse engineer the design." But, he said, it can be done.

https://edition.cnn.com/2022/07/23/politics/fbi-investigatio...