It was embarrassing.
I was about to go to sleep, and my carbon monoxide alarm went off. I opened a window and called 311 since I figured the City ought to send someone to check if the building is emitting odorless toxic gasses.
311 transferred me to 911, 911 transferred me to the fire department (literally two blocks away from my apartment). I told the fire department it probably wasn't a big deal, but my CO alarm was going off.
They told me they'd send someone to come look at it. That was an understatement. They sent a fire truck with ladders and stuff. I heard its sirens from a block away. The truck pulled up to my building with horns and sirens a-blazing. I heard the clomp clomp of firement in their fire paraphenilia coming up four flights of stairs and met them at my apartment door.
They checked my apartment for carbon monoxide (no danger) and concluded the alarm was old and I should replace it. I was embarrassed and apologized for having troubled them.