Happens once every few months. I've learned to check the response of my cat's. If they aren't looking at the door, it's in my head.
Bonus: If someone is at my door at some ungodly hour, they might leave me alone.
It's pretty remarkable how real it sounds though, complete with being in the distance - just enough to make you think it came from somewhere else in the house (usually the front door) - it definitely takes a deliberate act of will to totally ignore it.
Since another commenter has mentioned a knock on a window (distinctly different sound), I wonder whether our brains just contextualize this to whatever is plausible.
Great idea about the cats, I'll try that!
I'm still quite often woken up suddenly by Starving Cat Syndrome.