A basic cat flap is basically a hole that you can put in your door so that your cat can come and leave as they like. This design is not very secure and gives burglars easy access. Consider upgrading to a model that is lockable or automated with more security https://fitting-a-cat-flap95643.mybjjblog.com/adding-a-cat-flap-to-your-bifold-doors-43914916