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
In: Technology
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).
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