Pretty cool stuff.
A couple years or so ago when I had more time on my hands, I put together a pretty nifty little battery operated, self-contained motion sensor device. It had a PIR sensor, piezo buzzer, and 9V battery.
The idea was that it could be a rapidly deployed "security" system that you could put on the other side of a door (interior or exterior) where maybe you are hiding out. In SHTF time, we could very possibly find ourselves hiding out in abandoned buildings, and it might be a useful tool. It would alert you of any significant movement (also had distance adjustment POT on it). There's probably something out there already though just like it.
