How the hell do they work? If you don't know what I'm talking about, its those things where... you go to a supermarket, buy stuff, and as you leave, you walk through those metal-detector like things at the exit.
Now lets say you go to a supermarket, buy a bag of chips, and leave, cool. Now lets say you go to a supermarket, and leave without paying for the chips, those anti-theft detectors go off, but HOW? Thats the question here. After you've payed for the bag of chips, nothing changes. The bag is left untouched, unmarked, and unchanged. So how do the detectors know if you've payed for the item???
Some clothing stores have those big tags stuck on the shirts, those are removed after you've payed for the clothing. But things at supermarkets and stuff don't have tags. If you go and pay for a basketball, nothing happens to the ball, nothing changes.
So how the hell do those things detect and know if your stealing an item???