There is no wait, it only locks if it finds some prey. Of course there are occasional false positives. But those are very rare (haven't compiled the exact statistics for that though).

The chase thing has happened, but since the door to get in is very small other cats don't tend to follow.

Since it's really cold here in the winter I also chose to design it so that the default mode is for the door to be open. So if there's a power outage it will always be open.

Regarding the weight thing. I don't think it's feasible unless your cat always brings in rabbits or something, the weight difference is so tiny. Too many variables come into play as well, temperature differences being one, a wet cat compared to a dry one and so on. Might work, might not :)

> I swear I've seen a similar project like a decade ago, somewhere.

Probably "Flo Control"[0]. There was a system to get a silhouette of the cat's head to identify whether it was carrying anything.

0. https://web.archive.org/web/20081014091109/http://www.quantu...

The author of the original article references Flo Control and uses it in his implementation.

To be specific. I only took the general idea from that project. That is, to match the cat head against a lit background to make it easy to get a good profile image.

None of the implementation has anything to do with that project however.

> I have an easier solution - weigh the cat on a pressure pad just before the flap - allow for variances of a few ounces but not much more.

A mouse weighs around 20 grams, or 0.7 ounces. That's about 0.5% of the weight of a cat.