This is a cat's door or a flap. If you have a cat, this is a must, especially if you are not at home the whole day. This door gives your cat the freedom to be inside or outside.
I don't have a cat, and I can't imagine if a cat is outside in the freezing winter. The cat's door is a hinged flap set into a door, wall, door or window. It allows your feline friends to enter and exit a house on their own without needing to get help from a human. You don't have to leave your door ajar and stops intruders from entering your house. You won't have to hear her meowing at night when you are warm in bed and refusing to get up and let her in or out.