As I was typing last night, I realized each of the keys on my keyboard (which is nice and loud) probably have a unique acoustical signiature. And if I did some audio processing on my laptop microphone, which is sitting right next to it, I could probably (with some degree of accuracy) determine what keys I was striking with no electrical malarkey at all!
So today I stumbled across this: “Sensitive Objects”. These guys take small sensors (accelerometers) and place them on any flat surface, and detect the unique acoustical signature produced when any section of the surface is touched.
I wonder if I could do a dirt-cheap version of this just by monitoring the input of a microphone with my computer? The detection would be very complex because you’d have to detect a given signature regardless of ambient noise. Additionally, if (say) you were using your desk, I suspect the signatures would change based on the location of other objects on the same surface. (If you have a laptop there or not, for example.) It would be a really interesting way to get some extra inputs to your computer, but I’m quite sure that it wouldn’t be worth the CPU cycles to do it. Anyway. Just tickled by the thought, I guess I’ll leave it at that :)