False smoke alarm soundings

[Mike4]

I have two smoke alarms in my hovel, both Fire Angel, model ST622. They are about six months old.

Late last night the downstairs alarm sounded a couple of times, and careful investigation revealed no hint of a fire. I'd not been cooking for several hours and the wood burner had gone out hours previously too.

Then at 3.30am I was rudely woken by the upstairs smoke alarm going off. I got up, searched around and again no smoke, no smell of smoke or any evidence of any sort of fire, nothing.

Now both alarms sounding suggests they were actually genuinely sensing *something*, but it was definitely not visible smoke, or any sort of smoke smell that my nose could detect. So I conclude they were all false alarms as nothing was on fire.

So my question is, what can set off a smoke alarm other than smoke?

One further point is these smoke alarms are described by Fire Angel as "smoke alarms" specifically, not fire or any other sort of alarm. But coincidentally I recently bought a CO2 monitor (yes CO2 not CO) and that, last night had crept up to 2,000ppm CO2 when the first alarm sounded, indicating a lack of air changes. Odd. Could that be related?

[wilbobob]

Spiders can set off optical detectors. Makers datasheet for your alarm says vacuum them with a brush attachment every 3 months. Like everbody does. It also says that this may set off the alarm, so don't be alarmed.
Our alarm man told us that motion sensors can be set off by spiders, and he finds that a spray of blue Raid flykiller around the sensor seems to stop the nuisance

[MrFoolish]

Optical smoke alarms are very sensitive to smoldering fires. You might not be able to see or smell it.

Given you had a detection on two different storeys and an increase in CO2 I'd take it reasonably seriously. Though I can't really suggest a cause. It might be worth you switching off every electrical appliance and seeing if your meter still ticks up - just to see if you've got a partial short in your wiring somewhere. Good luck!

[Watis]

Some models of Fire Angel smoke detectors have a known issue with low battery warnings, in my case about three years into their ten year warranty. Its a single ping rather than the full alarm - is that your experience?

Phone them up and arrange for a replacement. Both my original alarms have been replaced and, this year, one of those replacements had itself been replaced. Must be costing them a fortune!

Watis