Make held a weird gadget contest, and Rick Prescott's modified Nerf Vulcan EBF-25TM machine gun came in first place. It uses heat sensors to track the movement of warm-bodied intruders and fire at them:
An idea sparked in my mind one day while walking the toy gun isle in a store with my kid and later that evening learning of the workings of a thermopile array while surfing the internet. The result is this infrared seeking sentinel which joins a realistically priced infrared sensor to a realistically operatable Nerf® machine gun to create a slightly less deadly yet still highly deterring automated machine. Personally I have grand plans to deploy the infrared seeking sentinel facing the entrance of my work cubical in order to speed interaction with less desirable visitors.
Link via Great White Snark