I imagine the products themselves must be tagged in some way, or you could trick the system with sleight of hand (I don't think it's visually tracking what goes

I imagine the products themselves must be tagged in some way, or you could trick the system with sleight of hand (I don't think it's visually tracking what goes into your basket). In which case, I imagine there would be an alarm if a product floats out of the door, accompanied by a mysterious stranger while another shopper supposedly in the store is missing. Or rather than an alarm, they would probably just sort it out later and charge your card.