The "Chrysostom" Great Seal Bug, 1945, USSR, created by Léon Theremin, who also invented the early electronic musical instrument bearing his name. The bug remained installed in the US Embassador's office for 15 years, though it was recognised as a listening device in 1952.

https://hackaday.com/2015/12/08/theremins-bug/

https://www.algora.com/Algora_blog/2021/02/07/the-great-seal...

That's how the Soviets bugged the US embassy in Moscow. With a resonant circuit w/o a power source and a reflected RF beam.

It's not processing though? It's acting like a mirror or a polaroid? Do those process?...