How an RFID wristband actually works

The reader does all the work

A reader continuously emits an alternating electromagnetic field. When a band enters that field, the coil of wire inside it — the antenna, usually a flat spiral etched or wound around the inside of the band — has a current induced in it. That current is tiny, but it is enough to power the chip attached to the coil for a fraction of a second. The chip wakes up, does what it is asked, replies, and goes dead again when the band moves away. Nothing is stored, nothing is charged, and nothing degrades from use.

The reply is a disturbance, not a transmission

The band does not broadcast. It answers by changing how much energy it draws from the reader's own field — switching a load on and off very rapidly, which the reader detects as a modulation in the field it is generating. This is called load modulation, and it is why the range is short: the reader has to sense a small perturbation in its own much larger signal. Double the distance and that perturbation falls away sharply, which is why a band that works reliably on contact may not work at all at ten centimetres.

What the chip actually says

In the simplest case the chip returns a unique serial number fixed at manufacture, and your system looks that number up. In more capable chips there is also memory the property can write to, and access to it can require the reader to prove it holds the right key before anything is returned. Which of these your system uses is a decision made by your access-control platform, not by the band — and it is the thing that has to be established before bands are ordered.

Why bands fail, when they do

Almost never the chip. The overwhelming majority of dead wristbands are dead because the antenna has been broken — a hairline crack in the coil, usually at a flex point or where a rigid inlay meets a flexing band. The chip is a fleck of silicon a fraction of a millimetre across and is nearly indestructible in normal wear; the loop of fine conductor around it is not. That is why construction matters more than chip selection for durability, and why over-moulded and sealed-pocket constructions outlast pocketed ones.