Make Your Own Self-Tracking Sentry Gun [Video] - Winextra
It will only cost you about $110 for the parts but you will definitely have to have some good DIY skills in order to pull this off but should you think you are up to the task then you to could own your own self-tracking sentry gun that fires AirSoft pellets or paintballs.
Rudolph Labs’ Project Sentry Gun will require some Arduino knowledge along with some open source software and servos but in the end you’ll be the envy of your block as you set up your self-firing tracking sentry gun to ward off all those irritating salespeople.
The basic setup involves an Arduino for doing the controlling, two servos for movement, a third servo for pulling the trigger, a webcam for target detection, some sort of mount for it all, and then the target acquisition software of course.
To give you an idea of what you can expect when done Project Sentry has put together a bit of a video for you to enjoy.