For cats, scratching is as normal as purring. They do it no matter where they are. If they are outdoors, they will scratch trees and wooden posts. So for indoor cats, they will target sofas, cabinets, walls, and carpets.
Simply place the carpet cat scratch protector inside the doorway. When a cat tries to scratch the carpet through a closed door, its claws will no longer be able to grip the carpet and will slip off the unit. This way the cat loses interest and the destructive behavior is eliminated so you can sleep or go outside in peace.