That would have been quite a ways back.
There was a way to bug a room using IIRC a small resonant chamber (hidden in the target room, obviously) and a strong radio wave from outside. The bugger simply monitered the disruption to his radio beam from the chamber and got audio back. Required quite a strong radio beam; probably strong enough for some brains to notice.
Wouldn't work today; far too much RF about.
I saw this in a special about electronic spying a few years ago. I think it was the Russians who came up with it early in the 20th century.
Wade.
Q:Is it proper to eat cheeseburgers with your fingers?
A:No, the fingers should be eaten separately.
