Great Seal. The Soviets once managed to conceal a particularly hard-to-detect listening device in a wooden Great Seal of the United States that hung on the wall in the U.S. Embassy in Moscow. Link. Link. Leon Theremin, famous for inventing the musical instrument of the same name, invented the innovative device. Link.
Doesn’t really make anything Declan said less true, though that is a pretty neat trick there. Consider that he said for the most part.
Here is an article about SOSUS an array of hydrophones to listen to Russian subs. I was interested when this came out because I was offered a job at Bell Labs on this project in 1980. They told me they were listening to whales and other stuff.