Standard detection and circuitry, but for the actual "alarm" part, the lid on a container of dry-ice is opened and humid air is blown through it causing fog to billow out from the engine compartment and underneath the vehicle: the would-be thief (or anybody else getting too close) will think that the car is going to catch on fire and runs away... and if they don't, the car is easy enough to track.

User-settable parameters include sensitivity, humidity/blower-speed, exposure timer and a paging option.
-- FlyingToaster, Feb 01 2009

What about having it go straight into the car? That way, he won't be able to drive it and since it is only cold CO2, it shouldn't damage the interior when there's a false alarm.
-- Bad Jim, Feb 01 2009


Going inside is the only option. Outside would be invisible in any wind or at speed and if visible would attract the attension of the fire department who may damage the car more than the theif.
-- MisterQED, Feb 01 2009



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