The hard plastic lump clipped to the hem of a new jumper does one job and one job only: it makes a noise if it leaves the shop. It does not know what the jumper is. It does not know the price, the size or the colour. It is not tracking you, it has no battery, and in almost every case it contains no ink. It is a small radio resonator, a bit of tuned metal that reacts when it passes through the pedestals at the door, and the person on the till takes it off with a magnet in about half a second.
That is the whole of it. The tag is deliberately stupid, because stupid is cheap and cheap is what lets a retailer put one on every coat in the building. Which raises the more interesting questions. What is inside that plastic, why does the pin never pull out, why do the gates sometimes beep at the wrong person, and what actually happens if you get home and find one still attached? Let us follow a single tag from the factory floor to your kitchen table.
The tag goes on before the shop ever sees it
Twenty years ago a stockroom assistant clipped tags on by hand. Today most large retailers use source tagging: the tag is fitted at the factory or the distribution centre, so the garment reaches the shop floor already protected, and no rail of untagged stock ever sits out on display.
What you are looking at is called electronic article surveillance, or EAS. That name matters, because EAS is a completely different thing from the technology most people assume is involved. It came out of the 1960s, long before anything digital was cheap, and it has barely changed since, because it does not need to.
What is actually inside the plastic
Crack one open, which you should not do, and you will find something disappointingly simple. There are two competing designs on British high streets.
The first is radio frequency, or RF, and it is a flat coil of wire connected to a small capacitor, which is a component that stores a little electrical charge. Together they form a circuit tuned to resonate at 8.2 megahertz. Think of it as a tuning fork for radio waves. Hit it with the right frequency and it sings back.
The second is acousto-magnetic, or AM, and it is more elegant. Inside is a strip of alloy that physically vibrates in a magnetic field, next to a magnetised strip that sets the pitch. The gates send a pulse at 58 kilohertz, then go quiet and listen. The strip rings on for a few milliseconds after the pulse stops, like a struck bell, and the gate hears it in the silence. Because it listens in the gap rather than through its own transmission, AM shrugs off interference that would swamp RF, which is why supermarkets use it. RF is cheaper and dominates fashion.
Neither type carries an identity. Every RF tag in Britain is tuned to the same 8.2 megahertz. Every AM tag rings at the same 58 kilohertz. The gate cannot tell a jumper from a jacket from a bottle of gin. It knows one thing: something live went past.
Why the pin will not come out
The pin pushed through the fabric is held by a ball clutch, a tiny cone containing three or four steel ball bearings pressed inward by a spring. Push the pin in and the balls roll aside. Pull it back and they wedge tighter, exactly like a cable tie. Brute force will not open it, it will only tear the garment, which is rather the point.
The detacher pad on the counter is a very strong permanent magnet, usually neodymium, that pulls the ball bearings outward against their spring so the pin slides free. Standard tags release at around 12,000 gauss, and retailers plagued by stolen detachers move to stronger locks. When an assistant thumps a tag against the pad twice, they are just getting the geometry right, because the magnet has to sit directly under the clutch.
The ink question
Most hard tags contain nothing but plastic and a resonator. A minority, called benefit denial tags, do carry small glass vials of permanent dye, and they are usually easy to spot because the dye reservoirs show as coloured dots or fins on the tag body. The logic is blunt: if the thief cannot wear the coat without ruining it, stealing it gains them nothing.
They are less common in the UK than the internet suggests, partly because a burst dye vial in a fitting room is an expensive mess and partly because retailers do not love the optics. If you have a plain round or square tag with no coloured capsules visible, you almost certainly have no ink to worry about. Either way, do not try to prise it open at home.
The gates at the door, and the innocent beep
The two pedestals you walk between are a transmitter and a receiver, sweeping their frequency and listening for a tag answering back. When they hear one they beep, flash and, in some stores, quietly log the time so the shop can see when losses cluster.
Now, why perfectly honest people set them off. Soft EAS labels, the flat white stickers on packaging, are not removed at the till but deactivated: a pad at the checkout kills the tuned circuit so it can no longer resonate. That is not always complete. A label slightly off the pad, or held at an awkward angle, can survive with just enough response to trip a sensitive gate three shops down the road.
Then there is everything else that happens to resonate near 8.2 megahertz: certain metal objects, some cosmetic packaging, occasionally a medical device. Retailers know. They tune the gates below maximum sensitivity, accepting that they will miss some real thefts rather than accuse a customer every four minutes. False alarms are not a bug, they are a commercial setting chosen with a spreadsheet.
The newer tag that does know what it is
Alongside the old EAS lump, a second kind of tag has quietly taken over British clothing retail, and it is the one people confuse with the first. Look at the swing ticket on a new item from Marks and Spencer, Zara, Primark, John Lewis or Decathlon and you will often find a paper label with a fine metallic antenna printed inside it. That is an RFID tag, short for radio frequency identification, and unlike the plastic one it carries a unique serial number for that exact garment.
This is what lets a shop assistant wave a handheld reader along a rail and count a thousand items a minute, or tell you in seconds whether the size 10 exists in the stockroom. Marks and Spencer was one of the earliest large adopters in the world, and our piece on how M&S handled the technical challenges is a decent read on what that took. If you want to know what is physically inside one of those labels, we pulled one apart in anatomy of an RFID tag.
Some retailers now use these RFID labels for security too, replacing the old gates with readers that can announce not just that something left, but exactly which item it was. The plastic tag is slowly on its way out. It will take years.
What happens if you get home with one still on
First, nothing. It is not transmitting, it is not tracking you and nobody is coming. It has no power source and it is inert unless it is standing between two pedestals.
Take it back with your receipt and any assistant will remove it in seconds. The same chain helps, because detachers are keyed by strength and type, but you rarely need the exact branch. What you should not do is attack it with pliers, a lighter or a screwdriver. You will destroy the garment, and if it is one of the ink versions you will destroy it spectacularly.
And if the alarm goes off while you are walking out of a shop you have done nothing wrong in: stop, smile, show the receipt. Staff deal with this constantly. In England and Wales the police recorded 530,643 shoplifting offences in the year to March 2025, the highest since current records began, and the British Retail Consortium counted 5.5 million detected incidents costing retailers close to £400 million. Against numbers like that, the gates stay switched on and slightly over-eager, and the rest of us occasionally get beeped at.
Frequently asked questions
Do security tags on clothes track you?
No. A standard EAS tag has no battery, no serial number and no memory. It responds to a specific radio frequency at the shop door and is inert everywhere else. Even the newer RFID labels, which do carry a serial number, can only be read from a few metres by a purpose built reader, and there is no network of them outside shops.
What happens if I leave a shop with a security tag still attached?
The alarm may sound as you pass the gates. If it does, show your receipt and staff will remove the tag. If you get home and find it, take it back to any branch of the same retailer with proof of purchase and they will take it off. There is no penalty and no record kept against you.
Do all security tags contain ink?
No, and most do not. Ink tags are a specific product called benefit denial, and they usually show visible dye capsules on the body of the tag. Plain tags with no coloured vials contain only a resonating circuit.
Why did the alarm go off when I had not stolen anything?
Almost always a label from an earlier purchase that was not fully deactivated, or an object that happens to resonate near the same frequency.
Can a magnet remove a security tag at home?
A sufficiently strong magnet will release a standard clutch, which is precisely why retailers increasingly fit higher strength locks that domestic magnets cannot open. Trying it on an ink tag risks ruining the garment.
What is the difference between the plastic tag and the paper label with a metal pattern?
The plastic tag is EAS, an alarm device that knows nothing. The paper label with the printed antenna is RFID, which carries a unique number for that individual item and is used for stock counting as well as security.
We explain the everyday technology hiding in plain sight, one piece at a time. Join the RFID News newsletter for the next one, or browse everything we have written about RFID in retail.
