I was under the impression that pet microchips have an incredibly short read range, like you have to actually rub against the reader, and on target. The cat would have to be already passing through the door to be scanned. Are they just jacking up the transmission power, which makes me wonder why all the existing chip readers wouldn't do that as well if possible?

I briefly looked at building such a chip reader until I saw the disance specs and realized it wasn't going to be practical to train a cat to rub the mid/back part of its neck on some protruding antenna