Reading the chip, not the collar
A microchip pet door works off the same rice-grain-sized microchip your vet implanted between your dog's shoulder blades, the one already used for identification. The flap has a built-in scanner in its frame that constantly checks for an approved chip within range, usually 10 to 15 centimetres. When your dog walks up and the chip's unique ID matches one stored in the door's memory, a motor unlocks the flap for a few seconds so they can push through, then it locks again automatically. No collar tag, no battery on the dog, nothing to lose in the yard.
Registering your dog with the door
Most microchip pet doors are programmed the same way: put the unit into pairing mode, hold your dog near the sensor until it beeps or flashes, and the door stores that chip number as an authorised entry. Most units hold anywhere from one to 40 registered pets, which matters if you have several animals or a multi-dog household. If your dog was chipped years ago at a different clinic, that's fine, the door doesn't care who implanted the chip or when, only that the number is readable and unique.
Selective entry, unlocked exit
Nearly every microchip door on the market only restricts entry. Your dog can always push out to the yard, and the locking mechanism only engages on the way back in. That's a deliberate safety choice: a dog should never be trapped outside, but you want control over what wanders in. Some higher-end models add a curfew or "in-only" mode you can schedule for overnight, plus a manual override so you can lock the flap completely during fireworks, a storm, or when the yard has visitors.
What can still get through
A microchip door reads the chip, not the animal, so a stray cat with no chip is blocked, and a neighbourhood cat wearing a competing RFID collar tag (rather than an implanted chip) generally won't trigger it either unless you've specifically registered that collar's tag with a compatible unit. The gap owners run into is a chip that's migrated slightly under the skin, sitting outside the sensor's read window, or a battery-powered flap left in a damp spot where the electronics fail. Test the door regularly rather than assuming it still works after months of quiet operation.
Power, weather and reliability
These doors run on batteries or a plug-in transformer, and battery life varies a lot by brand and usage, so a low-battery warning is worth checking on a set schedule. Because the sensor and motor sit in the frame, exterior-rated doors are built to handle rain and temperature swings, but a door mounted somewhere it gets direct hosing or standing water will fail faster than one under an eave. If reliability matters for your household, a model with a physical backup key or manual lock override avoids the day the electronics glitch and your dog is stuck outside a locked flap.
When to loop in your vet
If your dog isn't microchipped yet, that's a five-minute in-clinic procedure and it's worth doing before you buy a chip-reading door, since the two features rely on each other. Confirm your chip's registration is current with the national pet registry too, separate from the door's own memory, since a lost dog is identified from that database, not from the door in your kitchen wall.
