Joking aside, mostly likely overpowered microwave espionage equipment they got from Russians a long time ago, and that is still in use.
Google "US Embassy microwave moscow" to find out what happened back in the 70s.
yes, Theremin invented it, but the patent and production is from American firms. and cmon, if you're bugging a high profile country diplomat, you don't make a bugging device with a freaking opening mechanism!
if that were indeed from Russians, it would have been at least glued shut and not have a hinge.
Please don't insinuate that someone hasn't read an article. "Did you even read the article? It mentions that" can be shortened to "The article mentions that."
It actually does directly mention microwaves:
> The Russian security services were also known to flood the U.S. embassy in Moscow with electromagnetic radiation. They would beam concentrated microwaves and electronic pulses at the Embassy in an attempt to eavesdrop on U.S. typewriters and conversations.