[fluentbyfire]

For me, it's a loud knocking on the door. It's as if impatient cops were knocking. It's not a pounding sound, it's knuckles to wood. I immediately awaken to check if someone is there, but no one ever is.

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.

[voiceblue]

Happens to me as well. Now I just ignore a knock on the door (or rather, most any sound) if it happens just once as I'm waking up. It has been a hallucination every time.

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.

[DonHopkins]

Like the East German Cold War Stasi Era version of my Washington DC Reagan Era Nuking World Syndrome.

Great idea about the cats, I'll try that!

I'm still quite often woken up suddenly by Starving Cat Syndrome.

[dghughes]

Just don't get a white cat with blue eyes (they're deaf).

[Euphorbium]

Same happened to me a few times, I also heard knocking on window, while on the 5’th floor.