chirping smoke alarm? Saw a YT clip of a dude hunting for annoying beep with army of audio recorders, turned out to be battery depleted fire alarm under the stairs.
Considered this too, but there are two reason I ruled it out:
1. The beep was very long - maybe a second or two - much longer than smoke alarms.
2. I could hear it blocks away from my apartment. No smoke alarm chirp would carry that far.
