Edit: to clarify. I’m talking about these vertical things near the entrance, which set an alarm off if you bring something unpaid for close
In: Technology
I’m not sure if I can write enough words for ELI5:
Sensors by the door don’t work for everything, it’s only certain high value items, such an item will have a little strip on them that the cashier passes over something several times to deactivate when you buy it. I guess the strip is probably an RF chip, but I’m not sure.
If you try to pilfer something that doesn’t have this tag, the alarm will not go off, but the store may or may not have other loss prevention measures such as people monitoring cameras that would watch you try to steal the other thing.
I would rephrase this question to ask how the sensor monitors in stores detect the theft sensors on items.
Depending on the store, they have a loss prevention department which monitors cameras throughout the store for any suspicious activity. A mom-and-pop store might not have this ability so its usually up to the employees to monitor for theft
The store doesn’t actually know you are stealing anything. The security guards at the store do. Because they weren’t born yesterday and have cameras.
What do you mean? If you are stopped and asked to show your pockets/bag etc? Or if an alarm goes off?
The simple answer is that those things by the door are huge antennas.
They constantly transmit a signal, and if that signal gets a response, they fire up an alarm.
The response they expect comes from a nifty type of passive radio chip that gets powered by the transmitted signal, and when they fire up they send out a signal of their own. A very elementary signal. Short. With barely any data content in it. But that’s alright. All the bars at the door have to do is to send a signal and listen for something in return.
The passive radio chips are so small that they can be put *on the backside of stickers*. It’s common that the actual price tag is also the alarm tag for the merchandise.
And then they come in the form of plastic tags that you attach with a needle to a piece of clothing (those tags also often contain a anti-tamper-feature that instantly soils the sweater with ink that can’t be washed off) and also in the form of a small plastic pin about the size of a paper-clip that is commonly used to protect small items such as DVD boxes.
And that is pretty much what there is to it. If you get too close to the alarm arches by the door, and they manage to activate one of the small radio chips so that it starts to transmit, it’ll sound an alarm.
There are sensors placed on products, which are removed or deactivated during the checkout process. If you try to walk out without paying, then they sensor will not have been deactivated and set off the alarm.
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