We were watching History Detectives tonight, and there was a bit on Léon Theremin. I had heard of his eponymous instrument before, but what I did not know was that Theremin used his invention as a ploy to steal industrial secrets for the Soviet. He used his contacts in RCA to tour plants and meet engineers and scientists, all of which was then carefully documented.
Theremin playing a Theremin
In addition to this, Theremin designed what later became known as The Thing. The Thing was an amazingly clever bug that was concealed in a wooden Great Seal of the United States that hung in the US embassy in Moscow.
It worked much like an RFID tag, it had no power source of its own, but rather coupled with a powerful microwave emission to produce a signal when a diaphragm moved. The mechanism is beautifully simple. A truly great engineer designed this. The linked article has a lot of good technical details for those interested in this kind of thing.