> A simple speaker and microphone is all you need to make a functioning motion sensor. You could just use an infrared motion sensor. They are dirt cheap and wi

> A simple speaker and microphone is all you need to make a functioning motion sensor. You could just use an infrared motion sensor. They are dirt cheap and widely used for controlling lights. The AC unit at work has one, too. So, all of this already exists. Without spying capabilities, that is.