In this video, I build a laser microphone, a device that can pick up sound from a distance using just a laser and receiver. This technology was first used during the Cold War by the KGB and is still used today. By shining a laser beam at a window, sound waves inside the room cause tiny vibrations that modulate the reflected light. Using a photodiode sensor and an amplifier circuit, we can convert those fluctuations into audio. I’ll be testing this homemade laser microphone to see if it actually works for listening through windows.