“The Thing also known as the Great Seal Bug. On 4th August, 1945, a group of Soviet school children presented to W. Averell Harriman (The US Ambassador to the USSR) with a carved US Seal as gesture of friendship. It hung in his office for 7 years before discovering it contained a listening device.”

I had the full briefing on this back in my Agency days. The listening device had no power of its own. The Soviets beamed a microwave frequency at it, the chamber inside resonated and was modulated with the voices inside the office.

For its time, this was exceedingly clever and advanced technology.

I happened to be in Moscow when the Soviets were building an embassy for us. It include concrete riddled with semiconductor parts so that our bug detectors would not work. One side of the building had a duct the vertical length of the building that was actually an antenna. It was very innovative. We eventually tore the building down and started over.