I’m coming in late here, but I just wanted to mention that there have been a couple of community members who took a regular smartthings – compatible motion sensor, put a small tube over the lens to make the detection field very narrow, and then mounted it at shoulder height for an adult so it catches them just as they walk through the door frame into the room.
@Mike_Maxwell Did a lot with these, and had very good success. He would put the entire thing behind a plate in the wall just for aesthetic reasons, but in the following thread you can see the step-by-step project with the tube attached to just a regular motion sensor as he tests for the right location.
The trick is getting just the right height to catch the people that you want to catch without catching the dog. And of course if the dog jumps up in the air at just the right spot, it will also trigger it. So It can take some trial and error to get it right. But if you want to catch people walking through a doorway, and everybody in the house is taller than the dog, you can usually make it work. 
