Smoke alarm constantly going off

[SmokeAlarmARrRGGH]

The smoke alarm is going off constantly. It's been more than 2 hours. Not the full alarm but not chirping - a constant high pitched squeal...
We've pressed the hush/test button, cleaned it, hoovered it, replaced the batteries, turned the mains power off, removed the whole unit - and still it's going.
What else can we do?! I'm desperate to go to bed!

Is it stilll going off if u removed the batteries? Sounds like it’s gone faulty either that is not a carbon monoxide detector to is it . It can’t still make that noise if no batteries in it

If you’ve turned the mains off, and removed the battery, what is powering it?!

Yep still going off without batteries and when the mains was switched off.

I have no idea what's powering it any more! It feels like a form of torture!!!

Did anyone else immediately think of this? 😁 Sorry, no advice OP.

Not a carbon monoxide alarm. It's a linked smoke alarm - 3 on the same system but only the one on the top floor going off. Have replaced batteries in all 3 though.

Yes exactly this!!!

Wrap it up in a couple of big towels and hide it at the back of the garden.
Tomorrow go and get a replacement because it sounds like this one isn't working properly anymore.
Then destroy the defective one with a hammer.

This happened to me once at about 3am!. I just wrapped it in towels and shoved it under sofa cushions to muffle sound til the morning. I moved another alarm from somewhere else to make sure the thing wasn't alerting me to something - it wasnt, but didn't mean yours isn't. Though after 2 hours you'd hope they'd have reacted!

I have a connected fire alarm system & I remember it going off & I for the life of me couldn’t get it to stop. Nor could I get the bloody thing to detach from the ceiling, it was like 3/4 in the morning. I ended up having to take a broom to it 🤣

Found this it does say it might be the alarm itself that has malfunctioned so do what the last person said smash it outside https://www.businessinsider.com/guides/home/smoke-detector-beeping

Percussive maintenance is needed. With a hammer.

I had this once and nearly dismantled the entire house trying to shut the thing up. It turned out that the noise was actually the carbon monoxide alarm on the bookcase in the same room. The noise from the alarm was completely non-directional so we had no idea where it was coming from. When I figured out that it was a different alarm making it, I just removed the batteries and the noise stopped.

Even when we take it off the ceiling and turn the power off something in the base unit is still making a noise. The main unit that you take off isn't making a noise so no point throwing it in the garden. Everything we've googled says this shouldn't be happening but it is!

DH now thinks it's something in the wall cavity... But what?! And why?! I fear we've gone mad

Is it next doors alarm?

Definitely ours. Its much louder when stood directly under the alarm.

Maybe it’s the naughty elf that folk keep saying are doing naughty things in their houses lol

We're semi detached - fortunately it's on the detached side and our neighbours can't hear it.

Sorry I've no help to offer but DP had to have one to meet building regs when they had a loft extension done on a pre-existing side annexe. It was nothing but trouble, similar to what you describe, so DF ended up removing the unit entirely from the ceiling bracket and also removing the batteries from the unit.

I have since installed a basic standalone for peace of mind which hasn't been the slightest problem.

Agree with the hammer treatment. Works wonders.

Quoting myself as it seems that we've not gone mad!

DH has spoken to the alarm manufacturer - their alarms don't make this noise! He played them a recording.

Electrician has been - confirmed it's not the smoke alarm. He agrees that it's something in the wall or ceiling - possibly a carbon monoxide alarm but there's nothing visible that it could be. More exploratory work to happen tomorrow to try to find the source!

We've got a secondary carbon monoxide alarm and happy that it's something malfunctioning rather than us being poisoned.

I know you said it's not the smoke alarm now but in case anyone searches in future, mine did this
It's a wired one with battery back up and it had reached the end of its life basically! I had to replace the unit

Put new batteries in

Read the OP and the updates!