First Review of Nest Protect: Why You Still Need a Carbon Monoxide (CO) Detector

This week, Nest, the company that created the progressive Nest Thermostat, revealed its new gizmo - the Nest Protect. As our readers know, we’re big fans of the Nest thermostat for three reasons: it’s a truly great thermostat; it has set a new (and much needed) standard for product design in the energy efficiency sector; and it’s a terrific “add on” service for the home performance contracting community we serve at Energy Circle.

So when the Nesters announced their second big thing, we were immediately excited. Scheduled for release next month, the Nest Protect is a smoke and carbon monoxide detector with a host of impressive features. It will connect with smart phones to send alerts, speak to us, and detect its environment using six different sensors. Needless to say, it’s gotten lots of attention; it’s an overdue movement toward integrating smart technology in our homes with a particular aim at one critical but annoying and enigmatic product--the smoke detector. Really smart move by Nest. Revamp a product that every home is required to have, that is universally problematic and badly designed, and apply the usual Nest design magic. On this score, it certainly seems to live up to the hype. But the Protect is a Carbon Monoxide (CO) monitor too, and though the smoke alarm part of it has received all the attention, we wanted to look deeper at the CO component. On this dimension, we’re sad to say that Nest Protect has fallen short.

Nest Protect has made no apparent advances in carbon monoxide detection. If you’re unfamiliar with the dangers of CO, let’s just say they’re worth investigating. Catastrophic releases of CO in a home, usually from some home performance related  problem like poorly ventilated appliances or bad ventilation, kills people. But what indoor air quality and home performance experts are increasingly focused on is the issue of long term exposure to CO at low levels--the kind that kill you slowly instead of right away. A number of recent, credible studies have pointed to very harmful effects as a result of long-term exposure to low levels of CO. And detector standards in the U.S. - set by the Underwriters Laboratories (UL) - simply do not account for chronic exposure.

The UL’s current permissible exposure limit to CO requires detectors to begin emitting audible alarms after a time weighted average (TWA) of 70 ppm (parts per million) over 60 minutes. As TWAs reach higher tiers (150 ppm and 400 ppm), duration before alarm decreases. It’s a flawed system that only protects us from spikes in CO levels. Putting the numbers in perspective, long-term concentrations as low as 5 ppm have been linked to serious birth defects. And the health threats multiply dangerously before UL standards intervene, particularly in children and other at-risk persons. The safety measures are simply outdated, yet CO detectors continue to follow them. To our dismay, such is the case with Nest Protect.

What we draw from this is that Nest Protect, unfortunately, will not be a substitute for low level CO detectors (which we highly recommend, by the way). And, sadly, we worry that just as homeowners are starting to understand the importance of measuring low level CO, along comes the most credible, trusted company in home gadgetry with a product that doesn’t go the extra mile. Millions of people will undoubtedly buy the Protect. And most of those won’t know that the CO monitoring component is limited.

We’ll continue to dig in to the guts of the Nest Protect to figure out where they sourced the carbond monoxide CO sensor and whether there’s a solid economic reason for not going low level. So far none of the literature provides any details, and the cutaway image only shows a picture of the sensor. If we find out more, we’ll report.

Low level, long-term exposure to carbon monoxide is a very serious public health threat, and one that we wish got more attention from Nest. Still, the Nest Protect is an exciting and pioneering device that brings positive attention to the realm of home performance. In all likelihood, one will find a home here at Energy Circle.

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Hi Conrad,

Allison Bailes (EnergyVanguard) wrote a great article on this topic nearly a year ago. The bottom line is that UL's requirements for listing a CO detector product seem to exclude those devices capable of detecting low levels of CO.

And it appears the reason why is that many municipalities fought low level detection levels, over fear of too many nuisance alarms resulting in calls to fire departments or other responders.

In other words, if Nest Protect offered low level CO detection, it wouldn't have qualified to be a UL listed device.

The article is here; the comment thread makes for an informative read:
- John

For the cost of more than $200, Nest should offer low level CO detection.

It is amazing that about 75% of the homes we upgrade do not have already have CO alarms installed. To think that local building codes have not mandated them to date is astonishing, given the documented harm that low level CO exposure can do. To see UL only concerned with high levels is disappointing, to say the least.

Peter Troast's picture

Thanks for chiming in guys. 

@John: we definitely should have pointed out and linked to Allison's piece. It's excellent as usual.

@Dan: clearly, like Apple, Nest is a premium product company. By all counts, it appears their $250 thermostat has been enormously successful, but I know in our house we can only afford one zone. For us that works, but in the case of smoke alarms, where you're supposed to have on in every bedroom, outside every bedroom and on every floor, $129 x __ is going to be pricey. 

We're all in agreement that the lack of low level CO is dissappointing. But given all the UL issues and local code fears that John points out, not to mention the revelations that the CO sensor has a lifespan of 7 years but isn't replaceable as a standalone, you have to wonder if CO is Nest's tar baby.

Peter, you bring up a strong point in pricing multiple units at the smoke alarm level....maybe Nest could be encouraged to address the low level CO alarm market with a stand alone product? hmm...

FWIW, the Kidde KN-COPP-3 seems like a decent poor-man's version of a low-level CO detector - and one that's UL listed, at that. You press a button to get the peak value measured - I've seen it down around 11 to 14ppm at times.

Since it's UL-listed and can also display low levels, I wonder if the Nest really would have been prevented from doing something similar. i.e. keep all the audible alarm thresholds as UL-mandated, but show a graph of the low-level concentrations in the app, or something along those lines. Who knows, maybe they still can add that...

Eric, I ran into another product similar to what Kidde offers at the recent ACI Conference. The UL Approved Defender Detector CA6050 offers detection of levels as low as 10 PPM with a touch of a button. My problem with all of this is that elderly, children and pregnant mothers should be afforded an alarm, rather than being forced to touch a button. Defender also has a LL6070 which detects 5 PPM and higher but is not UL approved, so to pass building code you have to install a low level (still forced to push a button) and then an additional UL approved alarm. There has to be a better way to protect all parties involved.

Hello Dan, I am a sales rep at Seaco Company, a distributor of Defender Detectors. I was using google to see what was being posted about the Defender LL6070 in particular and ran across your comment. You are correct on both counts in regards to the CA6050 and the LL6070. I agree with you that it is sad that UL does not allow the displaying of levels lower than 30 ppm without pressing a button. Just to clarify though, the LL6070 low level CO monitor does not need a button to be pushed for the current ambient CO level to be displayed. Once an ambient CO level reaches 5 ppm the current levels are automatically displayed until the CO levels drop below 5 ppm again. I am not quite sure if that is what you meant in your comment above, but I thought I would clarify that point. Anyhow, I'm glad you noticed the Defender product at the ACI conference, we are all very excited about this particular product line.

Peter Troast's picture

@Dan and @Sean--

Thank you both for chiming in about alternative low level CO monitors. The information about these products, and the frustrating UL standards, make it hard to know what to buy. 

In addition to the two of you, Bill Spohn of TruTech Tools is also a big fan of the Defender products, and he's someone I trust implicitly. 

Here's the link to buy the Defender LL6070 Low Level Carbon Monoxide Monitor from TruTech Tools. 

Personally, I'm hoping to find one under the Christmas tree. 

Sean, I would like to order a some of these for installation during home performance upgrades that we complete. Can you help me with this?

Further clarifying, I believe people should be provided some sort of audible sound when low levels reach a threatening threshold. It just doesn't make sense to me that at-risk people are forced to read a display, with so much technology readily available.


I would be happy to help you with your needs. You can reach me at

Also, to clarify, the Defender CA6050 CO Alarm that is UL Listed will display the current CO level from 10 ppm, the peak level from 10 ppm, and the duration of the peak level in minutes when you press the "Display CO Level" button. Most UL Listed CO alarms with a digital readout will only display the peak CO level, and no other data.

The Defender LL6070 Low Level CO Monitor will automatically display CO levels detected of 5 ppm or more. At 10 ppm, the monitor will also flash a red LED. At 15 ppm or more, the current CO level will be displayed, the red LED will flash, and the horn will sound.

Defender recommends that you install the CA6050 where necessary to meet local code, and then supplement with the LL6070 at least in the master bedroom and within the bedrooms where an infant or elderly person resides, if not throughout the dwelling.

Does anyone know if the Nest reports sensed PPM of CO (higher levels aside)? I can't seem to find any screenshots of the app showing a PPM reading that triggered the sensor. I assume it has a 1ppm resolution?

Charles, I installed 4 Nest Protects earlier this week. There is no digital display indicating ppm levels. The alarm emits a verbal warning and has a circle in the middle that lights up different colors based upon the level of danger. The Protect's are very nice, I especially like that if one goes off they all do, but I stand by my previously stated concerns.

Thanks - I know there is no digital display on the unit, but I was wondering if it was reported and displayed on the app.

There's no ppm or similar display on the app. I asked Nest support about such a thing and got a stock reply about "no, we don't offer that."

Energy Circle,

Thanks for the post on the new Nest product. Perhaps with enough nudging they will come out with a low level one.

Great job as always,

Dan Thomsen

Building Doctors

Peter Troast's picture

Thanks Kevin. Excellent.

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