Cat flap that I never got around to fitting, but it has been used
It can be better trained to read the microchip in your cat, or cats so that the flap will only let your cats in or out. No instructions but Google will find something.
Also 3 extension tubes that allow you to fit the flap in a cavity wall instead of a door
Cat flap (Bray SL6)
This offer has been gifted to someone and is no longer available.