An RFID key fob is a passive wireless tag that uses electromagnetic induction to transmit a unique ID to a compatible reader — no battery required. The two main standards are 125kHz (cheap, widely used, low security — can be cloned) and 13.56MHz (more secure, NFC-compatible, encrypted). For most small business and residential access systems, 125kHz fobs at $20–$30 per 100-pack are the right choice.
How Does an RFID Key Fob Work?
Inside every RFID fob is a small coiled antenna and a microchip. When you bring the fob close to a reader (typically within 1–10cm), the reader broadcasts a radio signal that powers the chip through electromagnetic induction — like wireless charging, but for data. The chip responds by broadcasting its unique ID number. The reader compares this ID against an access list stored in the controller and opens the door if there's a match.
Because the chip requires no battery, RFID fobs are extremely reliable — they can last 10+ years without any maintenance. They only fail if the chip is physically cracked or the antenna is severed.
125kHz vs. 13.56MHz: Which Standard Do You Need?
| Feature | 125kHz (Low Frequency) | 13.56MHz (High Frequency / NFC) |
|---|---|---|
| Common Formats | EM4100, HID Prox 125, Indala, AWID | MIFARE Classic, MIFARE DESFire, HID iCLASS, NFC |
| Read Range | 2–15cm | Up to 10cm (NFC), up to 1m (some readers) |
| Security | Low — ID only, no encryption | Medium to High — encrypted options available |
| Can Be Cloned? | Yes (easily with ~$20 duplicator) | Depends — MIFARE Classic: sometimes; DESFire: No |
| NFC Phone Compatible | No | Yes |
| Cost per 100 fobs | $20–$30 | $40–$80 |
| Best Use Case | Apartments, gyms, low-risk offices | Healthcare, corporate, government, high security |