If the number is 15 digits — the FDX-B standard — every flap we review reads it; 9 and 10-digit numbers are older standards that only some models accept.
It is a two-minute check that decides which flaps are even candidates.
The standards
15 digits is FDX-B, the modern European standard. 9 and 10-digit numbers are older types. PetSafe’s flap specifies 15-digit chips; SureFlap’s range also reads older formats and offers an RFID collar tag as a fallback.
When the chip reads badly
Chips migrate under the skin, and some sit too deep for a flap’s antenna. That shows up as intermittent entry rather than outright refusal — and a collar tag solves most of these cases for a tenth of the price of a new door.
Before cutting a hole
Read the chip, choose the flap, then measure the wall. In that order.
If the cat has no chip
Collar-tag doors exist and work the same way, with the tag as the key. The trade is that a collar can be lost, and on a cat it must break away under load.
This does not replace your device’s manual. Blade temperatures, locking mechanisms and cleaning procedures differ from model to model, and the manufacturer’s instructions take precedence over anything written here. Unplug a device before dismantling it, check a hot blade or an air nozzle against your own hand before it goes anywhere near an animal, and keep a mechanism that closes or rotates under supervision until you know how it behaves.
The questions owners ask
Where do I find the number?
On the registration paperwork, or from any vet, who can read it in seconds with a scanner.
Last reviewed 2026-08-17