I recall reading somewhere that airports use natural gas cannons to scare birds off the runway. Maybe you need the same thing on a motion detector inside your walls.

Our neighborhood has also installed some high-def camera equipment - we've had good success providing the cops with photos of burglary suspects - they say they appreciate the leads, although they haven't reliably converted them to convictions.

The camera combined with the propane cannon should provide some excellent YouTube material. ;)