That CO alarm is giving me a headache

OK, yes that is an old joke, but I do have a slight mystery over the CO alarm.

This first happened last year, and drove me round the bend. A chirp every 49 seconds. This is normally a smoke alarm with low battery.

The problem is that we have 8 alarms in the house, and trying to work out which is chirping is not as easy as it sounds, especially when it is 2am, as it always is with these tings.

I actually ended up replacing every battery and still had a chirp. I then remembered there is a smoke alarm in the loft, and replaced that, only then to realise it was the CO alarm  in the loft! I went to replace that and found it is mains only, and Ei3018 CO alarm. Annoyingly it continued to chirp for some time once removed from the power.

I actually ended up buying a new one, and has been fine for over a year.

Then this week, it happens again. Thankfully I remember the loft this time. What is extra odd is that when I opened the loft hatch, the chirping stopped!

The next night it started again and did not stop. So I removed it, and waited. I put back in place next day.

The next night it started again, so removed, and new one ordered.

But I decided to actually read the manual, and it is odd.

It did not alarm!

Now, a key thing here is, it did not alarm. I would know, I have been in the house all the time, it is linked to all the other alarms, and to a relay input to my alarm/monitoring system as well. It did not do an alarm, honest.

But the manual says it has a memory mode, where, for 24 hours after an alarm, it will chirp. There is however a problem with this.

1. It had not alarmed!
2. It stopped chirping when I opened the loft hatch, so was clearly not doing a 24 hour chirp.
3. It is a single chirp - the manual explains it does 2 or 3 chirps, etc, for different types of alarm.

However, reading further, the manual does have a single chirp every 48 seconds. This is for "AC mains off or low battery backup", or (with green LED) low battery backup. I do not think it had an LED on.

So it does indeed sounds like the backup battery is depleted and the action is "replace alarm".

But this is just over a year for a device that should last over 10 years, arrrg!

I wonder why?