What Is an RFID Card and How Does It Work?

RFID cards are behind most of the tap-and-go access control you encounter every day — office doors, car parks, gym turnstiles, hotel rooms. They look identical to a standard plastic card, but inside the card body there is a chip and an antenna that communicate wirelessly with a reader.

This guide explains exactly how they work, what the different types are, and how to specify the right one for your application.

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What RFID stands for
RFID stands for Radio Frequency Identification. It is a technology that uses radio waves to transfer data wirelessly between a card (or tag) and a reader. In the context of plastic cards, it means a card that communicates with a reader without any physical contact — no swipe, no insert, just a tap or a wave.

What is actually inside an RFID card?
An RFID card contains two components embedded inside the card body, sandwiched between the PVC layers during manufacture:

A chip (integrated circuit) — stores the card's data and handles communication with the reader.

An antenna — a flat coil of wire that harvests energy from the reader's radio field and transmits the chip's data back.

Neither component is visible from the outside. The card looks, feels, and prints exactly like any other plastic card. It can be printed on both sides with full colour artwork, finished with gloss or matte laminate, and produced to standard CR80 dimensions.

How does it actually work?
The process happens in milliseconds and requires no battery in the card:

1. The RFID reader constantly emits a radio frequency signal within a defined range.
2. When an RFID card enters that field, the antenna in the card harvests the electromagnetic energy.
3. That energy powers the chip, which modulates the radio signal to transmit its stored data back to the reader.
4. The reader decodes the response and passes the card's ID or data to the connected system — door controller, access software, loyalty platform, and so on.

This is called passive RFID — the card has no power source of its own and only activates when it enters a reader's field.

RFID frequencies — the most important thing to get right
RFID systems operate at different frequencies, and a card built for one frequency will not work with a reader built for another. There are two frequencies relevant to plastic cards:

125kHz (Low Frequency) — the older standard. Common formats include EM4100, HID Prox, and Indala. Typically read-only — the card stores a fixed ID number set at manufacture. Widely used in legacy office access control, car park barriers, and older gym entry systems. Cannot interact with smartphones.

13.56MHz (High Frequency / NFC) — the modern standard. Common formats include MIFARE Classic, MIFARE DESFire, and NTAG series. Supports read-write capability, encryption, and multiple applications on one card. Can interact directly with NFC-enabled smartphones. Used in contactless payment, modern access control, transport cards, and consumer-facing applications.

What data does an RFID card store?
The simplest RFID cards — such as 125kHz EM4100 — store only a fixed, read-only ID number, typically 32 or 64 bits. The system looks up that number in a database to determine access rights or identity. The card itself holds no information about permissions — those live in the software.

More sophisticated cards such as MIFARE DESFire have onboard memory that can store data in multiple sectors, support several applications on a single card, and use encryption to protect data both stored on the card and in transit between card and reader.

Common applications for RFID cards

Office and building access control — the most widespread use. Staff tap a card to unlock a door. The reader checks the card ID against an access control database.

Gym and leisure centre membership — members tap in at turnstiles or reception. The system logs attendance and verifies membership status.

Car park access — cards issued to permit holders for barrier or bollard control.

Hotel room keys — higher-end properties use RFID alongside or instead of magnetic stripe.

University and school ID cards — often combining access control, library use, and cashless payment on a single card.

Public transport — Oyster and similar contactless travel cards use 13.56MHz MIFARE chips.

What to specify when ordering RFID cards
"RFID card" is not specific enough to place an order. You need to confirm the chip format that matches your reader infrastructure:

125kHz EM4100 — basic legacy access control. Read-only.
125kHz HID Prox — for HID-compatible access control systems.
MIFARE Classic 1K — widely used 13.56MHz format. Good for loyalty and basic access control.
MIFARE DESFire EV2 / EV3 — high security, multi-application. Used in transport and secure ID.
NTAG213 / 215 / 216 — NFC standard. Ideal for smartphone-facing applications.

If you are not certain which format your system uses, check with your access control supplier before ordering. Cards cannot be re-chipped after printing.

Ready to order?
We supply RFID plastic cards in a range of chip formats, printed in England with free UK delivery. If you know what you need, get a quote and we will turn around a proof quickly. If you are unsure which chip format suits your system, get in touch and we will help you confirm the right specification before you commit.

View our plastic card printing options or contact us with your requirements.