How does an anti-shoplifting scanner know if you’ve bought the item?

Question

I read that the scanners at the doors of a store detect items with magnets and such but what I don’t understand is how it differentiates between items that have been paid for

In: Technology

Answer 1

There are stickers they put on products like razor blades, batteries, small items easy to put in a pocket, purse, etc. There is a pad at the checkout the clerk will run the sticker over to demagnetize the sticker. Not sure if big stores use much anymore due to self-checkouts.