They don’t see anything inside a bag.
The item has a tag in it – it could be magnetic or it could emit radio waves. Not *every* item is going to have it, usually it is things like more expensive clothing, electronics, etc. Most things at many stores *aren’t* going to have it, because it’s too expensive and they assume people aren’t going to steal a bag of oranges (or don’t care).
At the checkout register they have a special pad in the counter that they wipe the item/tag over several times, this removes the magnetism or deactivates the radio frequency. If you go through the anti-theft devices *without* deactivating it, then the magnetic field interacts with the device and it sounds an alarm.
It used to be even regular items would set it off like your phone or car keys, but they’ve become better over the years (or… maybe our phones and car keys are different).
Latest Answers