You know that sad wee beep...

[HirplesWithHaggis]

...battery powered smoke alarms etc emit, when the batteries are dying? What would make a hardwired alarm do that? We have vacuumed in case of dust and wiped down the exterior, but it is increasing in frequency.

Don’t they have a back up battery in them in case of power failure? Maybe that needs changing?

Back up battery needs changed?

Hard wired ones have to have a battery too so although you may not have been aware of it till now it will be there.

Don't think I've ever had a smoke alarm battery fail during normal waking hours

It's always just before bed or in the middle of sleep.

Are they specially trained..?

Yes Tyne

It's the back up battery inside the unit.

Thank you ladies, much appreciated. Will get dh on it in the morning.

Yes, only ever at night and only ever in the autumn. Spiders come in the house more in autumn and they crawl into them and set them off at 2am. They then wait until you have gone back to sleep and do it again.