Voice can be read off glass, w/a microwave. I know a group that caged a room thinking they were home free with the cage an a 1930's fan running. The look on their faces when they read the transcription was priceless, they swore it was via lip reading, until it was proved it was via microwave. Seems Uncle had to learn this lesson the hard way as well. The Russians ain't as dumb as most think they are,...