how do the sensory machines at the doors of big shopping chains work? how do they know when someone is walking out of the store without paying for the certain object

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how do the sensory machines at the doors of big shopping chains work? how do they know when someone is walking out of the store without paying for the certain object

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I may be wrong here but “experience” has taught me that the sensors only work on products that have some sort of device, whether it’s a dye pack or just the little metal strip inside the box somewhere. This probably isn’t much help because I don’t know exactly what relays that signal to the sensors. Even less help, when I was little I thought they were just metal detectors.

Generally, they don’t know that you’re carrying an item that was not sold. Instead, they just know that the sensor was not removed from the product you’re carrying or that is was not deactivated.

That said, some stores are equipped with RFID tags. In these instances, the systems are smart enough to know whether the individual EPC of the tag in your product was scanned by the cash register or not. That’s possible b/c the point-of-sale system records the individual EPC for every item sold. It can then relay that information to the exit readers. If you try to walk out with and EPC that has not been marked sold, the system will alarm.

The sensors are tied to radio tags on/in merchandise. Those big plastic tags on clothing or the extra tag inside some products need to be removed or deactivated or they’ll set off the alarms. If you look at a check out counter at places like Target, there’s often a big grey pad with a circle on it that a cashier will run a product over a few times before bagging. That deactivates the anti shoplifting sensor in said product so it doesn’t trigger the door alarm. Same goes for the plastic tag on clothing. It contains an RFID chip that sets off the alarm, so needs to be removed at the counter when the item is paid for.

The little plastic tabs on CD boxes, the barcode style stickers with wires in them, and the big tags on clothing.

They generate an electro magnetic field when you walk through the sensors at the doors. The sensors pick that up and sets the alarm off.

There are many ways to easily defeat them, and further explanation of how they work will allow people to figure those out.

Oh I got you okay they have tags that send out high frequencies that the towers “hear” and it sets them off. Printed bar codes dont set them off unless they have an RFID inside (one that does).
Don’t steal?
A lot of the time they don’t know though, like if two people walk out they’ll assume it’s whoever stops in confusion

RFID.

If the tag is not removed or deactivated, then walking between those separators on the exits will set off an alarm.

The separators are actually giant antennae, inducing a magnetic field between themselves. When a tag (which is just a small coil of wire, probably inside a sticker, strip or tag on the product that’s normally removed when you purchase it) enters the magnetic field, it induces a current in the tag. The tag itself is a tiny antenna and radio. When it powers up, it broadcasts a number over normal radio waves. That number is picked up by the door-antennae. If it’s one that’s not been deactivated at the checkout… it sets off the alarm.

Same way that your contactless credit card, travel cards, door entry systems, etc. work. The fobs/cards/tags are just a coil of wire, a small radio circuit and a programmed number. The “readers” are actually giant electromagnets inducing a magnetic field. The field causes electrical power to appear inside the tag’s antennae. This powers up the chip. The chip radios out a number, and that’s picked up by the reader on ordinary radio waves (e.g. 125KHz or 1.33MHz for most of them).