A basic cat flap is a hole that's in your door that enables your cat to come and go whenever they want. This design isn't particularly secure and allows burglars access to your home. You may also consider upgrading to a lockable or automated model that has enhanced security features. https://cat-flap-in-upvc-door-pan33193.luwebs.com/31409525/using-a-cat-flap-in-bifold-doors