We’ve all watched too many spy movies in our life probably and know what you can do with lasers, such as listening to conversations miles away. Well, it’s actually possible to do that (for those of you who don’t know) and here’s a guy who built one himself.
The idea is that sound from someone speaking will vibrate the window that is in the same room as them. If you bounce a laser beam from a 5mW laser module off the window the laser beam will be deflected slightly as the window vibrates. If you monitor this vibration you will be able to hear what is being said.