What if you're not home? It is for such occasions that cat flaps were invented. However, today's cat flaps either open for any cat, or they're RFID-based, and for that to work, you implant a chip into your cat, which I find utterly barbaric.

Now what could be a great improvement is a cat flap identifying your cat(s) and letting them in based on computer vision, instead of relying on implants. I'd pay good money for it, provided that it worked in all weather conditions and all cat conditions (a wet and dirty cat needs to get in even more than a dry and clean one but I expect false negatives in these scenarios.)