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.)
Implanting RFIDs in pets is extremely common, as a method for identifying them to return them to their owners if they are lost or injured[1]. I agree it would a little silly to get an implant strictly to open a pet door, but given that they are already often present, leveraging that to open the door seems like a pragmatic choice.
Another problem with cat flaps is that you can't always install one if you have a rental. I suggested a doggie door for my parent's house, they said they looked into it but you'd be amazed at just how much space they take up, and they couldn't find a good spot to put it.
A few years ago our dog got out (Stupid power company went though our back yard and opened our gate and let the dogs out). We put up signs and were looking for him. Someone took him to the vet to get him checked out and told the vet he had the dog for years and was just able to afford to take him in to get checked out. The vet scanned his chip and our information came up. They called us. The guy left the vet and left our dog there. He is a purebred pekingeses.
That is why it needs to be inside the animal. And yes that is a true story. And yes he was also wearing a collar with a nameplate and address on him, the guy replaced it with a different collar.
Yes. The this is the alternate way of doing it with the RFID flaps if for some reason your pet doesn't have a chip or there are issues reading it. Cats can lose collars though, many have a release mechanism so that if the collar gets caught the cat doesn't get stuck forever too.
If a collar sits comfortably on a cat's neck, the cat will remove the collar. If a collar sits very tightly on a cat's neck, it's somewhat uncomfortable.
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.)