Please note, this door is on the small side, if your cat is more than 4.5kg, please purchase the larger pet door which is also on this site.
 
SureFlap cat doors recognises the microchip already implanted in your cat, allowing safe, secure access to your pet and making unwanted visitors a thing of the past. It can store up to 32 microchips and is compatible with all common identification microchips. Simple one-button programming. 4-way manual lock allows locking to any combination of in/out. The SureFlap cat door requires 4 x AA batteries not included. Typical battery life is over 6 months, and in many cases, up to 12 months with normal use. A low battery indicator light will start to flash every 5 seconds when the batteries need changing. No need for a collar or tag. 
As is, this will go into a wooden door. Cut out size for wood is 165mm (W) x 171mm (H)
Glass Installation If you need to have a hole cut in a window, please ask a qualified glazier to do it, as cutting glass is a skilled job. If you need to get a hole cut in your window a circular hole with a diameter of 212mm is the ideal size. A mounting adaptor is suitable for covering holes from 210mm to 260mm.
The smallest size the cat will have to fit through is 142mm wide and 120 mm high. 
THIS DOOR USED TO BE AVAILABLE IN BOTH WHITE AND BROWN, HOWEVER BROWN HAS NOW BEEN DISCONTINUED. 

MEASUREMENTS 
Overall size = 210mm x 210mm 
Hole size = 165mm x 171mm W x H 
Flap Size/ The smallest size the cat will have to fit through is 142mm wide and 120 mm high. Please do check your cat will fit through this size, as you may need the Pet door (I also sell this). 

For installing into a wall 
multiple extenders can be stacked together to form a tunnel of any length, each tunnel adds 50mm of length 
Tunnel Interior 150x155mm 
Tunnel Exterior 159x164mm 
Tunnel if needed is $16.80 extra 
 
PLEASE NOTE - These cannot go into ranch sliders, they are too wide. Please take Sureflap's word on this, a number of people have thought "maybe theirs would be different". It never works, the doors will not be able to slide passed each other.