If you have a cat that likes to go outside, you might want to get a pet door. That way you won’t have to keep opening the door for your cat whether it wants to go inside or out.
Some pet doors allow anything to go in and out while others let you cat wear a special collar that only lets it through the pet door. Depending on where you live and what might wander into your house, you can buy the pet door that best suits your needs and keeps your cat happy because keeping your cat happy is what life is all about.