NC3D

Ok, I'm officially beaten. Removed power and there was enough residual juice in the caps to chirp twice, 45 seconds apart. Tried disconnecting the bell, no difference. So unless somebody has any ideas of what it might be, I've just disconnected the speaker until I can replace the whole unit. My mother can at least sleep in peace now. P.S. It wasn't the smoke alarm.

With the panel open and my ear about 12 inches away I can categorically say it is the alarm. Tried it now on just battery, just power, both and it continues.

Just disconnected the power, but kept the battery connected. Stopped for now - turned power back on and timing how long it is before it returns. I think we can safely say it's not a smoke alarm.

Yeah you'd think - though I didn't wait long enough to see if it was the caps. I reset the box to factory settings and it stayed quiet for about 12 hours and now it's back with a vengeance. You would expect it to be a low battery signal, but tried 2 different batteries (though don't know how much charge they have).

Don't be so dismissive - my Mother's alarm is doing the exact same thing. I too disconnected the power and the battery and the chirping still continues. Maybe it's the caps discharging but this is ridiculous. It is NOT a smoke alarm - give the guy SOME credit.