Nest Protect is useless for low-level carbon monoxide

Published on 29 May, 2019 by Michael Bishop

Categories: Smart home

Nest Protect is arguably the best smoke and carbon monoxide detector available. I installed one a few weeks ago — the detector and the app are user friendly and very pretty. In this article, I want to focus on its carbon monoxide detection.

Why is carbon monoxide bad for your health?

I can’t put this more clearly than OSHA: Carbon monoxide is bad for us because “it displaces oxygen in the blood and deprives the heart, brain and other vital organs of oxygen.” Yikes.

Carbon monoxide is poison

If you live in a city, there’s no getting around breathing in carbon monoxide. But this should be a very low level — the EPA requires that cities keep it below 9 parts per million (PPM).

Average carbon monoxide levels could be significantly higher that this EPA minimum inside your home.

While you’d probably get a headache or nausea if the carbon monoxide level is over 70PPM for several hours, its effect is less noticeable under that threshold. But it still has a negative health effect. Especially for pregnant women, small children, elders, and people with respiratory issues (our source here is Nest). The health effects at levels under 70PPM aren’t as clear to people who study this, but one source suggested it could cause mild grogginess whenever at home.


How does carbon monoxide build up in my home?

There are several ways carbon monoxide can build up in your home. The main way is natural gas or propane not burning completely in your stove / oven or air heater (by the way: if your stove flames are yellow at the end or don’t circle all the way around, your stove needs to be checked out because it isn’t burning the fuel completely).

Another way is a non-electric car left idling in a closed garage. Or (gasp) cooking with charcoal inside the home.

Homes are more air-tight now — that extra insulation and weatherproofing is great because it saves energy. But, as noted by Nest, a downside is that carbon monoxide will be trapped in the home longer. That makes keeping an eye on carbon monoxide levels that much more important.

What is Nest Protect's carbon monoxide threshold?

Nest Protect and other popular carbon monoxide alarms follow the UL safety-certification company’s “2034” rule — an alarm should sound if the carbon monoxide level is above 70 PPM for over an hour. Unfortunately, that rule also says an alarm can’t sound if that 70 PPM level isn’t reached (I assume because they decided the health and safety benefit doesn’t outweigh the obnoxiousness of more alarms).

That’s understandable, but it’s unfortunate that Nest (and the other smart-home smoke + carbon-monoxide alarms) provide no information about carbon monoxide levels under 70PPM in their apps.

I have a 4 year old. If carbon monoxide levels in my home regularly go over 30PPM, I’d like to know about it (and do something about it). There are monitors that show carbon monoxide levels down to 0.1 (here’s one example), but those are expensive stand-alone units that aren’t connected to the cloud and don’t show data trends over time.

Why not show low-level carbon monoxide in the app?

The Sense energy monitor provides this sort of insight for a home’s energy usage over time. They offer a simple clean user interface in their phone app and browser app. ...They provide the high-level insight so I don’t have to geek out with custom spreadsheets. If only Nest did the same thing with low-level carbon monoxide reporting.

Nest Protect is connected to Wi-Fi and collects real-time carbon monoxide data (an old Nest whitepaper says one of two factors considered is “ the amount of time that carbon monoxide has been detected.”)


Carbon monoxide levels at high enough levels for long enough time periods can kill. No doubt, Nest Protect and other carbon monoxide monitors save lives.

It’s too bad though that they aren’t taking health and safety to the next level by giving us the whole story on carbon monoxide in our homes.

Author: Michael Bishop

Michael's core purpose is to improve the customer experience around going solar. He primarily pursues this by writing articles and software at CutMyBill.