Clothing and inventory tags
The strip of foil in your T-shirt label. It doesn't just say "medium blue shirt" — it says which one.
Hold a clothing label or a big retailer's swing tag up to the light, and there's often a thin aluminium squiggle inside with a speck of a chip in the middle. That's a UHF RFID tag. It's probably the most common RFID tag on Earth, with tens of billions made every year, most of them for clothes.
The number it carries is an EPC, an Electronic Product Code. Reading it is a job for UHF and EPC Gen2. This page is about what the number means and what shops do with it.
#What the EPC says
A barcode (a GTIN) identifies a product: medium blue shirt, style 4021. Every one of those shirts has the same barcode.
An EPC usually identifies an item. The most common format, SGTIN (serialised GTIN), is the barcode number plus a serial: this medium blue shirt, not the one hanging next to it.
Try it with GS1's own example, or paste an EPC from a real tag:
SGTIN isn't the only scheme. The first byte of the EPC says which one it is:
| Scheme | Identifies | You'll see it on |
|---|---|---|
| SGTIN | one specific item | clothes, shoes, cosmetics |
| SSCC | one shipment | cartons and pallets |
| GRAI | a returnable asset | crates, kegs, roll cages |
| GIAI | a company's own asset | IT kit, tools, uniforms |
Some tags carry a brand's own private numbering instead. They're still EPC-shaped, but they only mean something to that company.
#Who writes it
Usually the brand, at the factory. Labels arrive pre-printed with a tag inside, and the label printer encodes each one with the next serial as it prints: this is called source tagging. Every tag also has a TID, a factory serial burned into the chip. Systems that care can check that an item's EPC and TID belong together, which makes copied labels easy to spot.
#A tag's life
- Factory: the label is printed, encoded and sewn on.
- Warehouse: cartons are read through the cardboard on the way in, so nobody has to open boxes to check what's inside.
- Shop floor: someone walks the store with a handheld and counts every item in about an hour, a job that used to take a team all night.
- Checkout: some shops let you drop the whole basket in a bin and read everything at once.
- Returns: the serial says whether this is the exact shirt the shop sold, or just one like it.
- Exit: some stores read tags at the door to spot unpaid items.
Each step can be logged as an event: what (which EPCs), when, where and why (received, sold, returned). GS1 standardised that too, as EPCIS, so different companies' systems can share the history.
#Why retailers bother
Without RFID, a typical store's stock records are only about two-thirds right. Retail studies regularly show RFID pushing that past 95%. That matters more than it sounds:
- "In stock online" is true. Click-and-collect only works if the shop knows the item is really there.
- Gaps get noticed. If the last medium went this morning, it gets refilled today, not next quarter.
- Shrink gets measured. You can't tackle what you can't count.
The same tags also travel on airline bags, race bibs, hospital and hotel laundry, and pallets in nearly every big warehouse.
#Privacy, briefly
A tag still on your shirt after you leave can be read by anyone with a UHF reader a few metres away. What they'd get is a product code and a serial: meaningless without the retailer's database, but stable, and stable numbers can be used to recognise things.
- Swing tags come off with the price tag, so cut them off.
- Sewn-in labels stay. Some retailers put the tag only on the removable ticket for exactly this reason.
- Gen2 can kill a tag permanently, and newer chips can hide part of their number (see UHF — 860–960 MHz). Not every shop uses either.
With UHF reader
Read a tag on something you own, copy the EPC (24 hex digits) and paste it into the decoder above. Then read the TID bank and see who made the chip.