Indoor Cat Door
I am trying to think when a person might buy an indoor cat door. I would bet that there are very few, if any, in the UK. Whereas a lot of people have cat flaps (indoor to outdoor cat door).
To be honest I had not considered one until I noticed that people do search for them.
It appears that the indoor cat door need not be the same sort of device as an indoor/outdoor cat door. This is because one use is to prevent a dog entering an area of the house that has been designated a cat only area.
If your dog is substantially larger than your cat, the indoor cat door need only be an opening (without flap) that is too small for a dog to pass through. This has been referred to as a “cat hole”. Poor description!
This might be in a wall or door and the area to which it provides access might be a utility area where there is cat food and litter.
A cat door under these circumstances would prevent the dog eating cat litter or eating the cat’s food. Yes, dogs can sometimes like to eat cat litter disgusting though that sounds.
Another way to use an indoor cat door is to allow access to say a garage where there is cat litter. The garage will be unheated and the cat door will allow access while preventing cold air from the garage entering the house.
Another use would be for access to a cat enclosure that is outside. The cat enclosure might be part of a conservatory so it would be an indoor cat door.
Petsmart sell the cat flap type indoor cat door (USA).
Pet Door, another US retailer sells the open small door type.
You can buy, what appears to be the same one through the Drs Foster and Smith website (USA only again).
The home that is very much tailored to the cat companion is more likely to have the indoor cat door. You can see one in this house: Cat House Designs.