A basic cat flap basically a hole that you can insert into your door to let your cat leave and come whenever they want. This design isn't extremely secure and could provide easy access to burglars. You may also want to look into upgrading to an automated or lockable model https://catflapinstallationnearme26814.creacionblog.com/30670316/adding-a-cat-flap-to-your-bifold-doors