Laser microphones were projects that also made their rounds through electronics magazines, mostly in the classifieds on the last few pages right next to the sea monkey adds.

These supposedly worked on the principal that peoples voices would create vibrations on window glass and that by shining a laser beam on said window, it was possible to demodulate the observed laser changes back into sound.

I heard rumors that certain 3 letter agencies used more powerful particle beams to penetrate heavy curtains and other sound dampening measures employed in embassies as counter surveillance. As I heard it, the curtains needed to be changed on a regular basis due to them becoming radioactive.

If these devices actually existed and miraculously worked I would be very impressed with the operators that managed to calibrate them, given all the unknown variables presented in the field.