Problem with First Alert Z-COMBO CO detector not reporting

I have three of the First Alert Z-Combo sensors (combo smoke and carbon monoxide detectors).

Two are working fine. When I test them every month, they report separately for the smoke and CO sensors.

But the third one only reports the smoke detector… I’ve tried resetting it. And then removing and re-paring it with my hub. No change. The beep pattern is the same as the other two, but ST doesn’t report anything about the CO sensor (other than it’s there).

It’s also the newest of the three with a manufacturing date in mid 2022.

Anyone know what’s up with this?

I have noticed the same thing, but don’t know why it happens.

My detectors from 2017 and 2019 both show smoke and CO on the detector and in the ST App when tested.

My detectors made in late 2021 and early 2022 both show smoke and CO on the detector, but only show smoke in the ST app when tested.

I don’t have a CO test gas for a real test.

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I have a very similar (the same?) issue - 3 of 4 here are fine, just one will not report CO. I can check the manufacturing date, if you think that’s part of it.



Very odd … as I have 4 of these :laughing:. 3 of them work fine, but the 4th (just re-connected it, after exclusion / inclusion) … the Smoke detector shows Clear, Battery info is fine, but Carbon monoxide detector never reports. I try to refresh, and I get a message about a connection error. Huh? I tried testing the device, it alerts just fine, so it’s connected. It’s only the Carbon monoxide detector that has issues reporting.

Any thoughts?


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Thanks! Will reply to that thread, keep it all together.

Carbon monoxide detector, right? I don’t think First Alert makes a CO2 (carbon dioxide) detector as it’s not toxic. But there are some made for use in aquaculture. :fish::tropical_fish::blowfish:

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That does seem to be the main difference. No idea why they changed it. (Unless they realized that they didn’t actually have a way to test the carbon monoxide detector and wanted to reduce their legal exposure.)

I believe my device is from 2019 … so it should still work, no?