A small sticker is placed on or hidden inside high theft items. Older systems used a strip of metal that can be magnetized and demagnetized. The cashier swipes the tag across a special spot on the counter and it demagnetizes it; if they don't demagnetize it it sets off the alarm at the store's entrance when you walk past it.

Not all items will do that but higher value items that are more likely to be stolen have barcodes with electronics on the back of them. When it's active, the detectors will beep when you lass through them. When you scan the item, it also deactivates the electronics and letd you walk through without sounding the alarm.

When I was younger I used to take the electronic barcodes off of items and try to land them in people's bags or their jacket hood so the alarm would go off when they leave.

It will Beep. There is a small chip on it, a so called RFID Chip, which stores just a small amount of data, the state I was paid or I was not paid. When the product is scanned, the state on the chip is changed. When the state of a product is I was not paid, the System goes BEEP. Other possibility with the RFID Chips, they only have the state I was not paid and when scanned they get a small electric charge and are therefore destroyed. So the System only BEEPs, if there is a Signal, not which signal.

Do you mean from a self-service unmanned store or a regular supermarket or convenient store?

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A Red Bull isn’t going to make the security system alarm go off. They only put tags on bigger more commonly stolen items. Most of the time if there is someone manning the door they’ll just wave you through unless you have unbagged items in your cart or any big ticket items.

RFID is of two (major) distinctions, active and passive. For most bar codes, it is passive. The laser hits it, it tells the reader the information encoded (there's details here that don't perfectly fit passive RFID always but they aren't important). This usually is to look up the object and price and after you pay the store uses that information for inventory management. The object does not know if it is sold by itself. For expensive things, the tag is active, and by this it means you don't have to hit it with a laser, it calls out when nearby a scanner eg the door. You could have passive ones read at the door and they are trying to figure that out but it is complicated to energize and read all the stuff in your cart accurately, not to mention very expensive today. Anyway, the active tag (or something behaving like active RFID) is removed or de-energized at checkout so it can't call out to/be detected by the machine and set off the alarm. A red bull tag won't do this, nor will 99% of most tags in most stores. Most tags are meant as a way to quickly identify and look up an item.

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