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

The store has to put stickers or anti shoplifting tags on the items, if bought they are either removed or made to no longer work. If that doesn’t happen scanner will go off.