OK, I am in Ireland but I assume security alarms work the same way. This one is old and wired.

I don’t actually use the alarm. But over the years if there was a power cut, the alarm would set off and I’d need to input the code to turn it off.

The last few days it started going off randomly. No power cut. First time there was a two hour distance between it going off. After that it could have been a few minutes to half an hour. Inputting the code turned the alarm off.

My electrician pal said it was a low dead battery. So he had an old one he didn’t know how old it was. He changed it and it didn’t ring for two days.. Until today..

It only happened once today, which was nearly 4 hours ago.

Anyways my electrician said he’d get a new battery.

But my question is, why would a low battery set the alarm off? I understand why it would when power is lost and then returns, as the alarm panel thinks that power was cut off and then sounds the alarm.

But why would a low battery sound the internal alarm?

There is an external sounder too but that only came on when I turned off the mains power and it just made a constant buzz/beep noise.

From Google, it would appear to my uneducated mind that if the battery was bad for the internal alarm, it would sound the outside alarm, not the inside one.