another-dave:
sounds overly complex (visual recognition). Back to RFID. What’s the upside of reading RFID further away then unlatching with a dumb sensor closer in? you still have to get the RFID in proximity of the reader which is the problem; not the time it takes to read it. If anything, I’d reverse it. With a dumb sensor triggering an RFID transponder when you get within a certain distance from the access point. No point Spewing out RF if it’s not needed. but you still have to get the RFID close to the transponderOT-That (pet door) is an excellent candidate for the application of simple resonant tank (stop-loss tag) detection.
-No batteries on the tag, infinite life (for tag, not pet).
-Clearly defined access point to scan for tag
-Simple task, have tag at access point, door unlocks. No tag, stays locked. Sorry Mr. raccoon, neighbors dog, scrawny crackhead burglar etc.
I agree it’s complex to implement, but it should also be the easiest to use as you won’t have to remember to bring anything and it won’t trigger if you’re on the other side of the door frame. That issue was also my reason for thinking out loud of moving the RFID reader further out.
At the expense of batteries and needing to wear or display it, you could do something like an RFID tag with led’s that could also solve the false triggering. Make a fob of sorts that picks up a pattern from the doorway and responds with its own led. A different response pattern in each fob would allow for individual identification.
I guess it depends on how much effort is expected from the person entering the room. Something less than stopping to swipe a card is my interpretation. What about holding something up or maybe displaying a QR or bar code from a cell phone?