This morning, I awoke to an incredible cacophony of electronic screeches. At first I thought "Fire Alarm/Smoke Detector!" But no, the sounds weren't coming from the ceiling, where those units are mounted.

I traced the screeching to the CO detectors which are plugged in to low wall sockets outside each bedroom. Yep, both of them were going off, and both were shrieking the same 4-beep-every-5-seconds code (which is different from the replace-battery beep sequence). I live somewhat of a split level, one CO detector is downstairs, the other is upstairs.

I unplugged both units and opened the windows, and plugged them back in. While the LEDs on both units glowed green, they did not emit any audibles signature.

So I need your help figuring out why they went off.

Couple of factors that might help your diagnosis:

I have been in this house for 1 year. The CO detectors have been here at least as long as I have and have never gone off before.

I was here in the wintertime and used the furnace to heat the house (with windows closed) for a couple months, the detectors never went off.

I normally keep some windows open on the second story.

Recently we've had huge forest fire about 18 miles away and there's been a lot of smoke in the air and even ash falling. There was enough smoke in the air to smell it inside the house when the windows were open. In response, I closed the windows and used the AC for the first time this year. I've had the windows closed and AC running intermittently for the past 48 hours (up until the point where I had to vent the house).

I did not have any appliances running when this occurred, nor was the stove or oven on.

The AC was set to cool, but wasn't running at the time.

Questions:

Can AC units cause CO buildup?

What about forest fires?

What else might cause CO buildup?

Thanks.

Incomplete combustion is the cause of CO, so a forest fire can create it - BUT, it would be so diffuse by the time it reached your house I doubt it would matter. I guess it depends on how many ppm or ppb it takes to set off your detectors...

I wonder if the detectors are set at some really low level that actually could never cause any physical harm ?

Never heard of AC causing it. Furnace could.

If they both went off it's not a false alarm. Maybe the fires but not the A/C.
Call the local fire department. If it's the fires I'm sure you aren't the only one.
As I'm sure you know, CO isn't something to mess around with.

Coming at this as a first responder but check to see if there is a date code on your device. Most CO detectors are only good for 5-7 years (as opposed to 10 for smoke alarms). If approaching or past the life span, they need to be replaced.

quote:

Originally posted by SBrooks: I wonder if the detectors are set at some really low level that actually could never cause any physical harm ?

Possible, but these are factory units and I can't change the threshold setting. I'd guess they're set at whatever the industry or legal standard is for PPM.

quote:

Originally posted by 220-9-er: Call the local fire department. If it's the fires I'm sure you aren't the only one.

I may call their non-emergency number and check. The only thing I can think of is the nearby forest fire putting so much smoke in the air and somehow it accumulated.

quote:

Originally posted by Frenchy1004:
Coming at this as a first responder but check to see if there is a date code on your device. Most CO detectors are only good for 5-7 years (as opposed to 10 for smoke alarms). If approaching or past the life span, they need to be replaced.

Date of manufacture (Kidde) is April 22nd, 2016. That makes sense because these were installed as part of the handover from the previous owner. Probably first plugged in ~September of 2016.

I wonder if they both actually were triggered, or maybe do they cross talk over house wiring or wirelessly like some smoke detectors and only one was actually triggered? I have no idea how you would tell though...
You could check and see if they are capable of that.

A quick google look-see shows that detectors use a combination of concentration over time. Low concentration over a very long period of time will cause an alarm, and a high concentration will cause an alarm much quicker...

Not sure that this helps any. I suppose the fire could have generated a very low concentration over a very long period of time and tripped the alarm in that fashion.

If they haven't gone off again since the reset - I would chalk it up to forest fire and not worry about it any more (especially since they are new detectors).

Are they the kind that sync to each other, so that one going off would cause the other to also go off? Push the test button on one and listen to the other.

What gas appliances do you have? Oven, dryer, water heater?
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quote:

Originally posted by SBrooks: A quick google look-see shows that detectors use a combination of concentration over time. Low concentration over a very long period of time will cause an alarm, and a high concentration will cause an alarm much quicker...

Not sure that this helps any. I suppose the fire could have generated a very low concentration over a very long period of time and tripped the alarm in that fashion.

If they haven't gone off again since the reset - I would chalk it up to forest fire and not worry about it any more (especially since they are new detectors).

That actually makes sense. Thanks. I did put a call into the local FD and got referred to their inspector's division (left a message, will update if I hear back from them).

quote:

Originally posted by Some Shot:
Are they the kind that sync to each other, so that one going off would cause the other to also go off? Push the test button on one and listen to the other.

What gas appliances do you have? Oven, dryer, water heater?
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Did punch the test button, these aren't the kind that talk to each other.

I have a gas furnace, oven and stove. None of the aforementioned were running at the time. Everything else is electric.

water heater not venting properly??

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quote:

Originally posted by Sig209:
water heater not venting properly??

Water heater is my first guess if it's gas. I suspect you have an actual alert as you have BOTH detectors going off.

Since they did not go off again after the reset, I's call your gas company and see if they can send someone out. Fire will come as well (and remember I'm a firefighter) but the gas company actually as a general rule has better equipment and better trained people when it comes to CO or gas leaks.

Don't screw around with CO.

quote:

Originally posted by Appliance Brad:

quote:

Originally posted by Sig209:
water heater not venting properly??

Water heater is my first guess if it's gas. I suspect you have an actual alert as you have BOTH detectors going off.

Since they did not go off again after the reset, I's call your gas company and see if they can send someone out. Fire will come as well (and remember I'm a firefighter) but the gas company actually as a general rule has better equipment and better trained people when it comes to CO or gas leaks.

Don't screw around with CO.

Water heater is natural gas powered. I will put a call into them when I get home (windows are open now so, should not be building up any CO).

quote:

Originally posted by LDD:

quote:

Originally posted by Appliance Brad:

quote:

Originally posted by Sig209:
water heater not venting properly??

Water heater is my first guess if it's gas. I suspect you have an actual alert as you have BOTH detectors going off.

Since they did not go off again after the reset, I's call your gas company and see if they can send someone out. Fire will come as well (and remember I'm a firefighter) but the gas company actually as a general rule has better equipment and better trained people when it comes to CO or gas leaks.

Don't screw around with CO.

Water heater is natural gas powered. I will put a call into them when I get home (windows are open now so, should not be building up any CO).

Hot water heater is very likely cause if they are alerting. Unplug and look at back it may have a listing for different beeps/lights. You can also google the owners manual by part number on the rear as well. Kidde has excellent tech support, you can call them as well. 1-800-880-6788.

CO detectors can be sensitive to other gases, and some off gassing of solvents. Does the home have an attached garage?

A bad draw from a conventional water heater is a solid theory.

quote:

Originally posted by arcwelder76:
CO detectors can be sensitive to other gases, and some off gassing of solvents. Does the home have an attached garage?

A bad draw from a conventional water heater is a solid theory.

This could be it, not sure what type of sensor they use but if they are just looking for flammable gases it could be picking up something else that's flammable.

Fire Department said it was likely a false positive as a result of the Eagle Creek fire.

Will call Natural Gas company tomorrow.

You might go out and remove the nest from the water-heater exhaust if its on the side of your house.
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Same thing happened to me, for no reason anyone could figure two co alarms went off at the same time, blew them out and it has not happened since.