One of the most chilling ideas in Orwell’s 1984 (among so many it’s difficult to single out any particular one) is microphones hidden in the countryside and behind a picture on the wall.
This sign in London is a joke. I hope.
See also Photoprompt #3.
Have ideas like this had their day?
On tv thrillers, the good guys always seem to be able to filter the recorded messages from the bad guys in order to hear background sounds — and from that work out where the call was made. Is that a realistic scenario?
Write a story in which audio surveillance is the most important element.