Anyone who has ever owned a cat knows that it can drive you crazy, especially when they come in, and they immediately want to come back out a few seconds later. Then you let them out and sometimes they even want to come back in, only to repeat the same annoying process. Believe it or not, there is actually a reason cats do this; they are actually controlling their territory, which they unfortunately like to do very often. So once they go outside to check their outer territory, they want to go back inside and check their inner territory, and it basically turns into an endless battle sometimes.
Installing a cat door is sure to end your days of frustration when your cat wants you to get up and open the door every few seconds. They can come and go as they please. Also, don't think that cat doors are only useful for exterior doors. It is a great idea to put cat doors in areas where there is a litter box and you want to keep your other pets (like dogs for example) out of that particular room. In this case, you would simply make a cat door small enough that only a real cat could get through.
Another thing you can do is install a cat door on a door that only leads to a porch, but doesn't actually let them out. They are likely happy just hearing and smelling the outside doors, which is the best thing about letting them out on the porch.
Car doors are very simple in operation. All they really are is a hole with a flexible rubber flap mounted on top of it, so that the flap hangs right in front of the hole. It is automatically sealed by powerful magnets built into the flap. So all your cat has to do is push against the flap and it will release from the magnets and then allow it to pass through the hole, from both sides of the door. After the cat passes through the flap, it will fall back behind her, and the magnets will hold the flap in place, keeping it nice and comfortable, and for the most part weather resistant.
However, if you live in a cold area, the flap may not be weather resistant enough; it's not actually thick enough (or made of the right material) to be a good insulator, although it does adhere well and fit and create good seals. In other words, it will let cold air through, at least in the dead of winter when it's very cold. Under normal or even moderately cold conditions, you probably won't even notice cold air coming through the cat door. And furthermore, the benefit of using a cat door will outweigh the possibility that it will let in a cold draft from time to time - at least people who have to deal with cats wanting to come and go every few seconds, https://www.affordablepetdoorsmelbourne.com.au/