In fact, a British intelligence agent cited lasers as a reason The Guardian's work reporting on NSA leaks might not be entirely secure even though the documents were entirely disconnected from networked computers:
He said by way of example that if there was a plastic cup in the room where the work was being carried out foreign agents could train a laser on it to pick up the vibrations of what was being said. Vibrations on windows could similarly be monitored remotely by laser.
Laser microphones work by bouncing a laser off of a window or other surface that will vibrate with the sound waves in a room. The laser beam is returned to a receiver where the vibrations are processed into sound.
The technology behind laser microphones was reportedly first developed by electronic musician and inventor Leon Theremin in the 1940s and quickly impressed into KGB service under the code name "Buran" or storm. According to Robert Kessler's "Secrets of the FBI", U.S. intelligence agencies were also using laser microphone techniques during the Cold War.
It was well known enough in the 1970s that a University of Baltimore Law Review referenced eavesdropping by lasers as a "virtually indetectable" snooping technique that can be carried out using invisible infra-red laser beams only a quarter of an inch thick.
The devices can be hard to deploy, because you need to set up in near perfect parallel or have a prism affixed to a window to line up the receiver. But once in place it is relatively hard to detect and doesn't require direct access to the inner sanctums of a target's home.
There are some methods for avoiding or detecting laser eavesdropping, including using textured glass or special coatings. A recent profile of Alex Karp, a co-founder of intelligence contractor Palantir reported his office uses gadgets known as acoustic transducers on all the window panes in his office to vibrate the glass with white noise to combat the deployment of laser microphones.