Carbon Monoxide Detectors for Emergencies

Carbon Monoxide Detectors for Emergencies


In the United States, some 50,000 people visit the emergency room every year as a result of carbon mon­­­­oxide poisoning. An informal investigation by Chicago’s CBS Channel 2 suggests expired CO alarms are a key factor. Out of 9 units gathered from volunteers, 7 failed when exposed to lethal amounts of carbon monoxide; all were over 5 years old. In a larger study published by the American Journal of Public Health, 12 out of 30 alarm detect­ors collected from volunteers failed; all but 2 were over 5 years old. In both studies, several homes had been relying on CO alarms that were over 14 years old.

Like any electronic device, CO alarms are subject to failure, but in contrast to many other devices includ­ing smoke alarms, CO detectors are comparatively short-lived. The electrochemical sensors in most res­idential alarms de­grade within 5 to 7 years. Some manufacturers now claim a 10-year lifetime, which is technically pos­sible for sensors produced since 2013 if the unit is consistently maintained in an ideal temperature and humidity environment.

Manu­facture instruc­tions suggest testing these devices monthly or even weekly, but it is likely that many never get tested at all. What’s more, the “push to test” button only tests the battery, circuitry, and buz­zer, not the electrochemical sensor itself. I’ll explain how to test the sensor further below, but to do that you first have to understand how the alarm is designed to work.

CO Concentration (Parts-Per-Million)

UL 2034 Alarm                       Response Times


0-29 ppm


@9 ppm – Possible health risks with long-term exposure.

30-69 ppm

30 days

@30 ppm – Hazardous for those with heart or respiratory illness, infants, elderly, and pregnant mothers.

70 - 149 ppm

60-240 minutes

@100 ppm – Headache and dizziness after 1-2 hours.

150-399 ppm

10-50 minutes

@200 ppm – Headache, dizziness, nausea, fatigue after 2-3 hours, followed by unconsciousness and eventual death.

>400 ppm

4-15 minutes

@400 ppm – Life threatening in 3 hours.

@800 ppm – Unconsciousness in 1 hour, death within 2-3 hours.

@3200 ppm – Unconsciousness in 30 minutes, death in 1 hour.

@6400 ppm – Death within 30 minutes.


Organizations and agencies focused on the long-term effects of low-level CO exposure, such as its im­pact on brain chemistry or high-risk individuals, have established more rigid standards. For instance, the World Health Organization (WHO) is one among other organizations that recommends no more than 35 ppm exposure for 1 hour. In contrast, you’ll note from the chart above that a UL 2034-compliant alarm will not sound until you’ve been exposed to that concentration for 30 days. At 8 hours of exposure, WHO recommends no more than 9 ppm, a level that would NEVER trigger your UL 2034 alarm.

Accordingly, user guides for UL 2034 alarms warn: “This device … may not fully safeguard individuals with specific medical conditions. Also, young children and household pets may be the first affected. You should take extra precautions to protect high-risk persons from CO exposure…. Consider using warning devices which provide audible and visual signals for carbon monoxide concentrations under 30 PPM.”

Digital Display

In other words, you’ll need a non-UL 2034, low-level CO monitor to display and alert at these levels since the stan­dard prohibits displaying CO levels under 30 ppm to reduce emer­gency calls. UL 2034 alarms equipped with a digital display, however, at least provide of a way of observing levels above 30 ppm that won’t sound the alarm for 30 days.

We highly recom­mend a portable, low-level, battery-operated detector with a digital display in addition to your home’s hard-wired sys­tem for a few different reasons. First, you can use it as a supplemental monitor in a room with a wood or gas stove or in the bedroom of a high risk fam­ily member such as a child. Sec­ond, you can use it while traveling to monitor CO levels in hotel rooms, campers/RVs, or house­boats. And third, in the event of a power outage, you can place it 7-8 feet away from your port­able emergency stove to monitor any escalating CO levels well before any UL 2034 alarm would trigger.      


Residential CO sensors don’t provide the accuracy of premium, calibration-enabled sensors used in industrial monitors cost­ing hundreds of dollars, but generally function within a tolerable margin of error so long as the sensor remains viable and unfouled. Temperature and humidity have the largest impact on accuracy. A steam­ing hot shower could set off the alarm by causing a CO over-read, while low temp­eratures can result in a CO under-read. This is particularly import­ant to our application. Since you’ll likely be cooking in a cold room during a winter power outage, actual CO levels could be much higher than the sensor is able to detect. Below 40°F, the detector essentially becomes non-functional.

Testing the Electrochemical Sensor

Now that you understand the restrictions imposed by UL 2034 and the impact of temperature and hum­idity on accur­acy, you can test your alarm sensor with a few matches, a small glass or metal cup, and a gallon-size Ziplock bag. Place the glass on its side within the Ziplock bag along with the CO detector. Light three matches, let them burn about ½ inch, then place them together in the cup and quickly seal the bag. Within about two minutes, the device should register about 400 ppm, activating the 4-15 minute alarm response window specified by UL 2034.

carbon monoxide

In my case, the unit failed “safe” as it alarmed about 37 sec­onds before another 4 minutes had elapsed. That’s of course preferable to failing “unsafe,” alarming after another 15 minutes. If the device is in active use, test the sen­sor twice a year, such as when you change the time on your clocks each spring and fall. If used only for emergen­cies, test it before putting it to use.

carbon monoxide

Sensor Fouling

To avoid fouling the electrochemical sensor, don’t expose it to high levels of chemical contamination. For instance, don’t allow auto exhaust, air fresheners, paint, or aerosols near the alarm, and move it to a remote location before staining or stripping floors or furniture, painting, or changing refrigerant. Note that such chemicals can also cause temporary readings that are not CO readings as most residential CO alarms are subject to cross-sensitivity.

Top UL 2034 Budget Pick

Our favorite budget pick is the Kidde 10-Year Sealed Lithium Battery Power CO Alarm with Digital Display C3010D. For around $35, this UL 2034-listed device displays CO levels above 30 ppm within 30% margin of error, suitable for most healthy adults. It is a highly-rated de­tector with a 10-year life and a 10-year limited warranty. As missing or dead batteries is the leading cause of alarm failure, we always opt for long-life, sealed lithium batteries when available. Runner-up in this category goes to the $33 First Alert CO710.

Top Pick for High Risk Individuals

If you need to protect older adults, pregnant women, young child­ren, or per­sons with medical condi­tions, we recommend the Fast & Low CO Mon­itor from Foren­sics Detectors. For around $65 it dis­plays CO levels as low as 10 ppm, compliant with the most rigid domestic and interna­tional air qual­ity standards. The device trig­gers an audible alarm at 25 ppm after 1 minute and has the fastest refresh rates and response times of any comp­et­itor in its class. Runner-up in this category goes to the $60 Kidde KN-COU-B, a non-UL 2034 version of the above-mentioned C3010D programmed to display CO levels below 30 ppm.


Summary of CO Detector Performance.

To capture the above results, we placed all three units in a glass pan with three extinguished matches and covered them with plastic wrap. Forensics Detectors took just over 30 seconds to begin reporting CO levels, followed by an alarm at 60 seconds.

The Kidde KN-COU-B began reporting at 74 seconds. In addition to displaying low levels of CO, this “ultra-sensitive” device has a faster refresh rate than its C3010D predecessor, but slower than Forensics Detectors.


The Kidde C3010D began reporting at 105 seconds. We included this unit in these tests sim­ply for informational pur­pos­es. As mentioned, UL 2034 devices are not in­tended for high-risk individuals. It took over 18 minutes to alarm at the dangerous level of 300 ppm, while lower levels take hours or even days.

The Kidde KN-COU-B finally alarmed at 9 minutes, a full 8 minutes after the Forensics Detectors 1-minute alarm. At lower concentrations this alarm can take over 8 hours to sound and will not sound for levels below 40 ppm, making it better suited for observation than alerting in our opinion.


A version of the Fast and Low CO Monitor containing lithium batteries will be available by mid-summer. Though the electro­chemical sensor is capable of a 10-year lifespan, the company expects many of these units will be put through demanding temperature and humidity extremes and has thus decided to lower the expected sensor lifetime to 5 years.

Forensics Detectors was established in 2017 out of concern for the lack of affordable and effective toxic gas alerting products. It was founded by Phd engineer Dr. Koz, who became aware of this need after US law firms began engaging him as a world-renowned expert consultant. Inventor of the world’s first ve­hicle car­bon mon­o­­xide sensor system, his award-winning analyzers have outperformed some of the world’s best sen­sors. His informative site contains links to his youtube channel and other innova­tive pro­ducts, such as a compact model that was awarded “Best Travel CO Detector” by

I’m grateful to Dr. Koz for spending a generous amount of time with me responding to my many ques­tions on this topic and for providing a final edit of this article. In learning of the intent of our research, he suggested that we also inform you of the elevated risk of CO exposure following natural disasters due to the potential for damaged flues, caps, furnaces, shields, heat exchangers, etc. He graciously offered to publish this writing on his website.


Slightly lighter than air and able to travel through drywall, this odorless killer is invisible to all human senses of perception. As such, the importance of effective carbon monoxide detection can­not be over-stated, just as an under­stand­ing of detector limita­tions can­not be over-emphasized. Our dry, Utah cli­mate can prematurely impact the moist sensors’ effectiveness, so consider replacing them every five years despite manufacturers’ warranty claims. Be cognizant of the flu-like symptoms associated with CO exposure. And know the ra­tion­ale behind UL 2034, so you can make complimentary provis­ions to safe­guard family mem­­bers now while simultaneously preparing for future emergencies. We’ve chosen to augment our whole-house alarm system with low-level CO alarms at 5’ on each level of the home and will ensure that our missionary children take one with them into the field.

Any combustion appliance, such as a water heater or furnace, is a persistent threat, but portable stoves pose an increased risk. If use of a portable gas or alcohol stove in­doors is ever considered due to a pro­long­ed power out­age, a portable, low-level CO alarm, especially one with a digital display, would be an indispensable asset and should be kept within 7-8 feet of the stove. That said, NEVER allow reliance up­on a CO detect­or as just­ifica­tion for skipping rule #1. Ven­tilation, even and esp­ecially in the middle of winter, is the single-most im­por­tant ac­tion you can take to facilitate com­plete com­­bustion and manage the effects of in­com­plete combus­tion, thereby re­duc­ing the like­lihood of car­bon monoxide exposure.


Week 14 of a series of articles on Emergency Cooking Preparedness, 2021-04-20
by Robbie & Gina Jackson