Will the PlexiDor Electronic keep my cats in while letting the dog out? No pet door can guarantee that the cats don’t go outside with the dog. The cat may not have a key to open the PlexiDor Electronic, but cats are fast and smart, and if they want to go outside, they’ll figure out that they can use the door with the dog. Some cats will run ahead of the dog, others hurry behind it, and some run under it. One solution could be to use an indoor electronic cat fence to keep the cats away from the door. Pet Stop and DogWatch make these types of systems.