Theremin, yes the same Theremin who built the instrument that made the Star Trek theme song famous, had a hand in espionage as well. Albeit not a willing one. Turns out his life is actually quite tragic.
In addition to that story, Adam Fabio takes a trip through the details of "The Thing", a bug installed in the US Embassy by the Soviet Union during the cold war.
It used no batteries, instead depending on a carrier frequency transmitted by the "listener", causing the resonant cavity to transmit back the audio from the room at a higher frequency. Pretty nifty, and so was the hiding place: a hand-carved wooden seal of the United States.
Read the full story at
Our thanks to Stephen, G7VFY for spotting this item