Strange sound, like a smoke alarm detector

[MN2theMax]

7. I had this happen last year

though the offending unit was in sight. It kept doing the double sound bursts, even after I put in fresh batteries.
The carbon monoxide detector had reached it's ten year limit and had to be replaced to make the sound stop.

But first you'll have to find the thing! Mine plugged directly into a wall outlet and had a backup battery. Good luck!