Why would all of the fire alarms in my house go off at the same time?

[KidsHappen]

We have thoroughly checked the house and there is no fire, smoke or anything else that should be setting them off. I seriously doubt that all the batteries would die at the same time. Any ideas?

[KSera]

If it’s hardwired, they’re designed that way. If one goes off, it sets them all off. You could’ve had a bug walk across the sensor or something like that. Do you have any sensors in a basement area?

sorry, that’s always such a shock. And usually in the middle of the night.

[KidsHappen]

We don't have a basement and as far as I know we don't have any bug either. I know that they have gone off individually before but I don't ever remember them all going off at the same time. 

[Pawz4me]

They'll do that if they're hardwired. It could be something as simple as dust or a bug in one of them, or it could be that a sensor is going bad and they need to be replaced. They're only good for ten years, max.

[Laura Corin]

36 minutes ago, KidsHappen said:

We have thoroughly checked the house and there is no fire, smoke or anything else that should be setting them off. I seriously doubt that all the batteries would die at the same time. Any ideas?

I would vacuum them all. Dust can set off one and that causes them all to go off if they are connected. 

[Katy]

Dust. Try vacuuming. But after 9-10 years they need replacing. 

[Myra]

29 minutes ago, Pawz4me said:

They'll do that if they're hardwired. It could be something as simple as dust or a bug in one of them, or it could be that a sensor is going bad and they need to be replaced. They're only good for ten years, max.

And, for some reason, my hardwired ones go off every so often because of humidity - go figure

[maize]

It's not online hardwired alarms that will go off together; some battery-operated alarms are now designed to connect to each other.

[marbel]

16 minutes ago, maize said:

It's not online hardwired alarms that will go off together; some battery-operated alarms are now designed to connect to each other.

Yes, ours are battery and are connected so they go off at the same time. That way a person who is in another part of the house is alerted that there's a problem.

[SanDiegoMom]

same - ours are battery connected and we tried figuring out which one was the one needing battery replacement but it sometimes took days of them going off again and again.  Or I should say nights.  Why would it go off during the day when it could go off at 2 am?

[Ausmumof3]

Yep as others have said they will all go off together so one is probably malfunctioning or had a spider in it 

[PaxEtLux]

 

Are these smoke detectors, or combination smoke detectors / carbon monoxide detectors?  If they aren't all connected together, and they can also warn about carbon monoxide, that's something that I'd want to look into.