2:30 a.m. - Chirp

Me and fire alarms, we do NOT get along.
When I first moved into my place, I turned them off because steam from a hot shower, cooking, or any and everything set those bastards off.
Fast forward to 2005 and an electric fire.
I now have a hardwired system that seems intent on driving me crazy.

If I forget for a minute to turn on the exhaust when I'm toasting spices for an indian dish or opening a hot oven...
MEEEEEMEEEEEEEEEEEEEEMEEEEEEEEEEMEEEEEEEEEEMEEEE
leading me to hit the exhaust switch, run into bedroom (where the sensor lives) and quickly fan around it on while standing on my bed with a manila file folder or plate.
A little annoying, but training me to hit the exhaust switch.

Lately though, its been chirping - just once - now and then - for no good goddamned reason.
It's not battery powered (although it does had a battery backup... hmmm...) so it's not letting me know its low.. is it?
It seems to happen at night - at first I thought it was a dream, but then I heard it again while conscious. It's what woke me up tonight - and it happened when there were those big thunderstorms a few days ago.

Theory: Bedroom micro-climate.
I have next to no cross-ventilation in my apartment.
Like most old homes, the air stifles and sits.
So I have an AC unit in the bedroom along with a fan on low to keep the room what some have deemed "meat-locker cold."
I promise you it is not, but I wonder if the heat in the attic fighting the cold in the room have any effect. Or maybe I'm simply searching for answers to the maddeningly inconsistent unexplainable chirps.

All I know is that every time I hear it - it reaches into my body and wreaks an unimaginable panic in my soul - I hope it's merely a weak backup battery - but it's a lithium battery - like all good unstable things, it requires a healthy dose of lithium to keep it going - but I digress....
I'm unsure of the size or power - and I have no idea how to disconnect it long enough to replace without going deaf. I'm guessing this one's for the landlords.

By WHY only at night?
I was in here ALL AFTERNOON knitting and watching Arrested Development on Hulu - Nuthin'.
2 frickin' a.m. and *CHIRP*

... maybe it's me.

New Year's Eve this year I stayed at a friend's whose alarms kept chirping... even with freshly changed batteries... and again I say "Hmmmmm....."

3 a.m. - I'm going back to bed - who's got bets on a 4:30 chirp?
Anyone?

UPDATE: 7 a.m. - thank goodness it was at a reasonable hour - let me tell you it gets me UP and OUT OF BED.