I had a "spooky" period where on many different nights within the previous month I would awaken, exactly at midnight.
I don't mean "midnight-ish"... I mean Midnight = 12:00:00 on the dot.
It was puzzling. How could this be??
Then one night, I was awake, already at midnight... I had an eye on my clock, wanting to experience the world awake at the exact 12:00:00 hour. to see if my periodic awakenings were externally sourced?
When it was 11:59:59... my clock hesitated its progression...
When 12:00:00 arrives, the stupid clock had to flip all the tabs at once, and it strained the little motor which kicked up a momentary fuss, then...
CLICK... a slightly delayed arrival of 12:00:00, With a tiny noise, you wouldn't notice, would normally be "background noise" if you weren't listening for it at that moment.
The clock was the culprit, waking me up.
Do we know the entirety of information about the events of the night? Could there have been something smelt or heard or vibration-felt.
Stuff does get "in" while sleeping, and dreams can "conform" or "include" those external sensings.
I had a vivid dream one night. In my dream, with some buddies, we had gotten up to some no good. Innocent reckless no good. (again, thats in the dream). In the dream, I am hunched over working on something, then get tapped on the shoulder by a cop. In the dream.
Which makes me jump. My whole body twitched. In real life, my body twitched.
There was a nurse tapping me on the shoulder to wake me to check my temperature. She didn't want to wake me, but I hadn't been laying still enough for her to check in my ear while asleep.
We had a good laugh, which hurt my new stitches.
But the point is... reality entered my dream... became the cause of the plotline.
My overall point... when "asleep"... we are asleep. Resting. Not completely "unconscious".
We know we are "hearing" while asleep, because sounds can be loud enough to break through and take our attention. But continually, we are hearing sounds, and dismissing them as ":less important". Exceptions?? Yelling moms, and alarm clocks (hopefully when set to do their job).
To be "evidence" all information would have to be known. There may be unknown information. To be "proof" external sources, and coincidence would have to both be ruled out conclusively.
You suggest you had "long long ago" been in a fire alarm situation.
A question to ask would be "On how many other nights have you dreamt of being in a fire alarm situation or scenarios, and not woken up to a fire alarm scenario?"... If that number is in the hundreds, then having one occur on a night when there is a fire, becomes much more likely.