This totally rocks. It's a Paintball sentry gun. It detects movement and then shoots whatever it is that moved. I... I don't know what else to say. I usually love to waffle on in these entries but frankly, to say anything else would be to dilute the grandeur.
Oh, and while we're on the subject of sentry guns, have this (albeit pretty old) video of what the turrets from the game 'Portal' get up to when no-one is watching (this won't make a great deal of sense if you haven't played the game and/or are not monstrously geeky. Fairly warned be ye).
I See You.