I think it only would be fair if you do get beeped on your way out of the store (and you have purchased your items), that the store would give you a store credit for 40% of what you purchased.
Since they have no problems tretaing you like a criminal, they should have no problem compensating you for your public embarassment.
If this was the case, maybe the management of these stores would make sure their equipment is working properly in the first place. We know they don't care about the customers, but they do care about profits.