It's wonderful that you're keeping your pet safe inside, but a guest or a handyman could easily leave the door open, or a screen could come loose from an open window. There's also a possibility that your house could be damaged in a heavy storm, flood, or other natural disaster, causing your cat to run away in fear. Pets can even be stolen - particularly purebred animals. No matter how closely you watch your favorite animal friend, there's always a chance they can get out, and if they don't have any ID, they will be extremely hard to find.