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What Is The Best Carbon Monoxide Detectors To Buy In 2020?

Carbon monoxide (CO) is an odorless, invisible gas that can be a "silent killer" in homes, cars, planes, and other enclosed spaces. A byproduct of combustion, CO enters a person's bloodstream and immediately attaches itself to red blood cells, essentially depriving the body of oxygen.

A high concentration of CO from car exhaust or a faulty gas furnace can cause death through asphyxiation. Lower concentrations can trigger flu-like symptoms and other medical conditions over time. The only effective way for homeowners to monitor carbon monoxide levels is to invest in one or more carbon monoxide detectors that "sniff" the air and sound an alarm when CO levels become hazardous.

Early carbon monoxide detectors were chemically treated pads that turned dark in the presence of CO. Modern versions are much more sophisticated. Many provide CO readings in PPMs (parts per million) and "peak level" measurements between readings. We examined dozens of carbon monoxide detectors. The top contenders on our shortlist provide accurate, reliable information to homeowners.

Top 5 Best Carbon Monoxide Detectors On The Market



Some carbon monoxide detectors are portable. (Professional installers and home inspectors frequently make use of these.) Others may be hardwired into a home's existing wiring. Some are powered by batteries; others plug into a wall outlet.

In this section of our review, we look closely at each contender's display panel, power supply, alarm system, and other elements. Most carbon monoxide detectors have a shelf life of five to seven years, but some don't last that long. Some require re-calibration or other servicing from time to time. We mention any known durability and maintenance issues here.


Early carbon monoxide detectors were chemical-soaked pads that turned dark in the presence of CO. They were not designed to provide concentration level data or other types of information. Modern CO detectors employ an electro-chemical process that "sniffs" the air regularly and converts CO into carbon dioxide (CO2) for analysis. The results are displayed in "parts per million" (PPM). An alarm sounds if the readings exceed a certain level over a period of time.

The best CO detectors protect people from two kinds of CO poisoning: low levels inhaled over a long period of time and high levels inhaled in a short period of time. In other words, a CO detector should be able to sense a slow leak from a faulty gas line and a sudden burst of CO from a car's exhaust pipe equally well. We examine the test controls for each shortlisted contender in this section of our review.


Some manufacturers combine carbon monoxide detectors with smoke alarms. This solves some problems but creates others. The proper placement of a dedicated CO detector is different from that of a smoke detector. Some CO detectors must be hardwired into the home by a professional electrician; others can be supplied with batteries and mounted on a wall.

Some CO detectors can be carried from location to location and propped up on a stand. In this section, we consider each contender's ease of use, addressing factors related to readability, alarm resetting, calibration, and minimum/maximum PPM ranges.


Detecting carbon monoxide before it reaches toxic levels is extremely important, but the risk of exposure varies from house to house. CO is a byproduct of fossil fuel combustion, so homeowners with gas-powered furnaces or wood-burning stoves are naturally at a higher risk than people who live in all-electric homes with good ventilation.

This means that some users could safely invest in an entry-level carbon monoxide detector, but others should consider purchasing a high-end model that can detect CO leaks caused by faulty vents or blocked chimney flues. Professionals who install or inspect machinery powered by fossil fuels will want to consider buying a commercial-grade carbon monoxide detector that is both portable and extremely accurate.

The carbon monoxide detectors on our shortlist run the gamut from entry-level to commercial-grade. We recommend buying the model that fits your specific needs.


Most Recommended Carbon Monoxide: Detailed Reviews 2020


The smoke alarm/carbon monoxide detector combination unit is a fairly recent development. The Nest Protect 2nd Gen Smoke + Carbon Monoxide Alarm is a shining example of that school of design. The advantage of this model is that homeowners do not have to purchase two separate monitors to address two separate hazards. The downside is that CO detection is almost treated as an afterthought, since smoke and fire damage occur far more often than toxic CO build-up.

The Nest Protect system relies on WiFi communication between two or more alarms and possibly a Nest thermostat. WiFi service is not a requirement, however. Each unit can be hardwired into a wall; a six-battery backup is available in the case of a power failure. We like the aesthetics of the housing and the motion-activated “night light” included with this model.

Because the manufacturer of the Nest Protect 2nd Gen Smoke + Carbon Monoxide Alarm appears to place more emphasis on the smoke-detection function, the CO detector controls and display are very basic. There is no actual way for users to get a CO reading in terms of PPM. Instead, the CO detector's alarm is automatically set to sound when CO levels remain elevated for a certain amount of time. This could mean low-level CO readings between 11 and 30 PPM over a period of days or high CO readings (450 PPM +) over a period of minutes or hours. It is safe to say that when the Nest Protect CO detector does sound an alarm, immediate ventilation and evacuation should follow.

The CO detector uses an electro-chemical process that periodically "sniffs" the air and converts carbon monoxide into carbon dioxide for analysis. The chemical responsible for this analysis loses potency over time, which is why most CO detectors have a lifespan of five to seven years. Notably, the Nest Protect 2nd Gen Smoke + Carbon Monoxide Alarm has an estimated lifespan of 10 years.


Even if you don't have WiFi service, the Nest Protect 2nd Gen Smoke + Carbon Monoxide Alarm is very easy to install and maintain. However, the system reaches a much higher level of functionality in homes with full WiFi capability. If two or more units are installed, they can communicate with each other and send that information to a smartphone. 

Owners can receive notifications (and turn off false alarms) from anywhere in the world. If the home uses gas or other fossil fuel as a heat source, a Nest Protect CO detector – when wired to a Nest thermostat – will shut off the entire HVAC system immediately.  Although the Nest Protect CO detector doesn't have a functional display for day-to-day readings, it does test the air quality at least 400 times a day and is programmed to sound an alarm the minute a toxic CO level is reached.

The Nest Protect 2nd Gen Smoke + Carbon Monoxide Alarm's retail price of may seem prohibitive at first, but that price includes a high-end smoke detector and wireless connection between the units. It can even be synced with a smartphone! Few smoke and CO detectors offer this much interactivity at this price point. 

If a home or apartment is built to code, there's a strong chance that it already contains at least one or two basic CO detectors. However, the Nest Protect 2nd Gen Smoke + Carbon Monoxide Alarm is a logical upgrade to existing air-monitoring systems and a great product suggestion for contractors who are custom-building a new house. A WiFi-enhanced smoke and CO detector like the Nest Protect brings definite peace of mind to homeowners.

  • Combination smoke alarm/CO detector.
  • Tests air at least 400 times per day.
  • Unit typically lasts for 10 years (longer than average).
  • Expensive.
  • CO readings are not given in PPM.

A thorough, interactive device that delivers definite peace of mind. The best available.

2. Sensorcon Inspector Carbon Monoxide

Some carbon monoxide detectors are designed primarily for homeowners. Others are meant for professionals such as home inspectors, pilots, truck drivers, and HVAC installers. The Sensorcon Inspector Carbon Monoxide Tester & Meter definitely belongs in that second category. The waterproof housing is especially rugged. Essentially, the Sensorcon Inspector is a real-time CO gas sniffer with the ability to provide "peak level" readings.

This is the kind of instrument a professional home inspector might carry into an unoccupied home on the market. Similarly, a pilot might keep this device in the cockpit for periodic air quality sampling. Although this is not a passive home CO detector, it could be used to verify or deny any suspicions of CO leaks in the home or workplace. The unit is powered by AA batteries (provided by the manufacturer) and is calibrated at the factory just before shipping.

The Sensorcon Inspector Carbon Monoxide Tester & Meter performs one task especially well: the real-time analysis of air quality. While other CO detectors don't register readings below 30 PPM or provide accurate readings above 450 PPM, the Sensorcon Inspector can record CO levels from 0 to 2,000+ PPM.

Considering how incredibly toxic a CO reading of 2,000 PPM would be to humans, we strongly urge users to wear respirators and other protective equipment before measuring CO levels of this magnitude. There are just two control buttons below the LCD display: one activates the previous "peak level" reading, and the other powers up the real-time gas sniffer and mutes the alarm. We wish the alarm itself were a little louder, but many users aren't depending on it for personal safety. The consumers who are likely to buy this detector would be more interested in the real-time CO data it provides. We find it to be more than suitable for that purpose.


The Sensorcon Inspector Carbon Monoxide Tester & Meter includes an alligator clip that allows users to attach it directly to their clothing or a lanyard. A home inspector could easily carry it from room to room, taking instant CO readings along the way. Pilots and long-distance truck drivers could store one in their cockpits or cabs and push a button to make sure CO from exhaust is not entering their cabin.

While most homeowners would probably prefer to install a standard CO detector, some may want a way to measure carbon monoxide levels in places that standard monitors can't reach, such as garages, mechanical rooms, and attics. Weighing only four ounces, the Sensorcon Inspector Carbon Monoxide Tester & Meter is truly one of the most portable CO detectors available today.

If CO detection is part of a person's job description, the Sensorcon Inspector Carbon Monoxide Tester & Meter's retail price of may not sound all that prohibitive. It is designed to provide two years of professional-level service before a manufacturer-suggested re-calibration becomes an issue. Even without a factory re-calibration, the Sensorcon Inspector performs admirably, although some accuracy could be sacrificed without it.

We do feel that the Sensorcon Inspector may be too much for average homeowners, though. (Plenty of CO detectors that are designed specifically for home use provide the same level of reliability at a much lower price.) This model is a "real-time" gas sniffer, not a long-term monitor of low-level CO infiltration in a home.

  • Lightweight and portable.
  • Gives extremely sensitive PPM readings.
  • Pricey.
  • Not designed for home use (although home use is possible).

Designed primarily for commercial applications, this professional-grade detector goes beyond what most homeowners need.

3. First Alert CO615 Dual Power Carbon Monoxide

Last update on 2020-08-13 PST - Details

Some carbon monoxide detectors are designed to be hardwired to the home; others are meant to be attached to a wall. The First Alert CO615 Dual Power Carbon Monoxide Plug-In Alarm has the flexibility to be plugged directly into a standard wall socket or hung on a wall. 

We appreciate this level of mobility, as some users may want to test specific areas (like the laundry room or basement) for increased levels of CO. The unit is powered by two AA batteries (included) as well as a 120-volt plug. The backlit display is set to show the most recent CO levels in PPM along with the level of remaining battery power. When the display button is pressed, the peak level of CO measured that day is displayed. 

However, this reading is automatically erased after 24 hours, which could be troubling for users who want to track CO concentrations over a period of days or weeks. The First Alert CO615 uses an electro-chemical process to measure CO in PPM. As such, it has a limited shelf life of five to seven years. An end-of-life chirping alarm signals the need for replacement. Speaking of noise, the detector's 85-decibel alarm will definitely awaken users if high levels of CO are detected. However, lower concentration levels (10-30 PPM) may not trigger it. This is why we recommend due diligence and daily CO peak level manual readings.

Like most CO detectors sold in the US, the First Alert CO615 Dual Power Carbon Monoxide Plug-In Alarm employs an electro-chemical process to detect ambient CO levels within a few hundred feet of the sensor.  Any carbon monoxide molecules in the air are first converted to less-harmful carbon dioxide (CO2) through a chemical treatment. That sample is then tested for CO density. The First Alert CO615 maintains a constant display of the current CO levels and the remaining battery power. Users have to press a button to switch to a "peak level" mode; this mode reveals the highest level of CO measured between automatic resets.

There is also a button that will test the ambient air on demand and silence any alarms, false or otherwise. A LED light glows green when CO levels have not reached toxic levels. It turns red when conditions are hazardous to humans.  We wish the First Alert's display contained more tangible information, such as a digital number instead of a low-to-high bar system. The CO levels in a room must reach 30-70 PPM over a number of hours in order to trigger the alarm – unless the user specifically presses the "peak level" button and notices a higher-than-average CO reading.


The First Alert CO615 Dual Power Carbon Monoxide Plug-In Alarm is extremely easy to install. Experts strongly recommend placing at least one unit on each floor and additional units near sleeping areas. While other CO detectors must be hardwired into a wall or permanently installed near a common source of CO emissions, the First Alert CO615 can be plugged directly into a standard outlet. It can also be mounted on a wall and energized by the included power cord. This flexibility allows users to test specific areas of concern, such as a laundry room with a gas dryer or a workshop with poor ventilation. The control buttons are easy to read and fairly self-explanatory.

A First Alert CO615 plugged into a standard outlet's bottom plug will not block the top plug, which means a user could still install a nightlight or other device in the same outlet.  An occasional test is all that is required to make sure the unit is functioning properly. An alarm will chirp whenever the detector's chemicals reach their expected end of life (EOL), which is approximately five to seven years. At that time, a replacement unit would need to be purchased.

Because of stringent building codes concerning CO detectors, many homes and apartments already contain at least one functioning carbon monoxide detector and/or smoke detector. However, purchasing additional CO monitors is never a bad idea, and with a retail price of just , the First Alert CO615 Dual Power Carbon Monoxide Plug-In Alarm is an affordable model users could install near bedrooms, laundry rooms, HVAC mechanical rooms, and other places where CO buildup is possible.

A portable model like the First Alert CO615 allows owners to take long-term CO readings in one area of the house and then move the detector to a different area. Replacing a hardwired, high-end CO detector could be an expensive proposition, but replacing a budget-priced CO detector like the First Alert CO615 Dual Power Carbon Monoxide Plug-In Alarm would be a much easier financial obligation to meet.

  • Portable and affordable.
  • May be plugged into a wall socket or operated via battery.
  • Alarm is not as loud for lower levels of CO.

A budget-priced device for those who want quality CO detection. The best deal available.

4. Kidde KN-COPP-B-LPM

The Kidde KN-COPP-B-LPM Battery-Operated Carbon Monoxide Alarm could be used as a stand-alone or wall-mounted CO detector. Some freestanding CO detectors have stability issues, but the Kidde KN-COPP-B-LPM is quite stable when placed on a nightstand, counter, or other flat surface. Mounting this unit on a wall is a fairly simple matter of installing two anchor plugs and sliding the unit's back bracket over them.

The Kidde KN-COPP-B-LPM is powered by three AA batteries which should be changed every year. Because it uses an electro-chemical process to analyze air quality, its lifespan is the expected five to seven years. Some owners invest in the Kidde KN-COPP-B-LPM in order to satisfy their state's stringent building codes. Indeed, this unit does meet the UL standards for CO monitoring. Its 85 decibels would definitely rouse a deep sleeper during an emergency.

We like the fact that the Kidde KN-COPP-B-LPM's control panel offers a button for everything! Other CO detectors of this type often employ multi-functional buttons that require users to tap through various options before they get the display they seek. 

The Kidde KN-COPP-B-LPM's display panel has a button dedicated to a maximum "peak level" reading between resets. Another button controls testing and resetting, and yet another controls the unit's power status. If CO levels reach toxic concentrations, an audible alarm sounds and a small light on the control panel begins to glow. The Kidde KN-COPP-B-LPM automatically "sniffs" the air every 15 seconds, then combines that sample with a tiny amount of concentrated sulfuric acid to measure concentrations of nitrogen, oxygen, and carbon monoxide. 

This result is displayed as a number in parts per million (PPM). The measurement takes into account the CO concentration levels over a period of time before activating an alarm. High concentrations of CO detected in a short amount of time should trigger an alarm within three minutes; lower concentrations would take longer to calculate


Because carbon monoxide mixes readily with the oxygen and nitrogen blend we call "air," it can build up just about anywhere in an enclosed house. Wall-mounted CO detectors have saved countless lives over the years, but portable CO detectors like the Kidde KN-COPP-B-LPM also do their part to protect owners. 

This model uses the same electro-chemical methodology as more expensive hardwired units and can be placed directly in areas where CO emissions are a real possibility (bedrooms, laundry rooms, mechanical rooms, bathrooms with gas-powered water heaters). Because the Kidde KN-COPP-B-LPM is cordless, it could be located anywhere in a room – not just near an electrical outlet. Battery installation is straightforward, and the battery cover will not close until all of the batteries are in place.  We praise the Kidde CO detector for its stability on flat surfaces; it can be placed on a nightstand or dresser just as a small alarm clock would be.

The Kidde KN-COPP-B-LPM Battery-Operated Carbon Monoxide Alarm's retail price of is right in line with other basic home CO detectors we examined, including the First Alert CO615 and X-Sense CO03M.  Instead of replacing expensive hardwired CO detectors when they reach their EOL (end of life), many homeowners are now investing in cheaper (but equally effective) battery-powered alternatives.

Even those who are completely satisfied with their original hardwired or plug-in CO detectors are purchasing these portable models to keep in RVs, boats with enclosed cabins, cars, and spare rooms. We endorse the Kidde KN-COPP-B-LPM Battery-Operated Carbon Monoxide Alarm for its proven stability and ease of operation. While most people recognize the immediate hazards of smoke and fire, they may not be aware of the threat excessive carbon monoxide poses. At such a low price, purchasing several Kidde KN-COPP-B-LPM Battery-Operated Carbon Monoxide Alarms for the home makes excellent sense.

  • Loud alarm.
  • Easy to use.
  • Stable on flat surfaces.
  • Alarm takes longer to sound for lower CO concentrations.

A loud, budget-priced unit that could be attached to a wall or propped in place.


Google Nest Protect Smoke + Carbon Monoxide Alarm, S3000BWES, 2nd Gen, Battery
3,970 Reviews
Google Nest Protect Smoke + Carbon Monoxide Alarm, S3000BWES, 2nd Gen, Battery
  • Phone Alerts: Nest Protect sends you a message when there’s a problem or the batteries run low.
  • Smoke and CO Locator: Nest Protect speaks up if there’s smoke or CO and tells you where it is, so you know what to do.
  • Detects CO: Carbon monoxide is an invisible, poisonous gas. Nest Protect tells you where it’s hiding.
  • A Light in the Dark: Usually Nest Protect has its light turned off, but when you walk underneath it, pathlight can light your way.
  • Fast Detection: Every second counts. The Split-Spectrum Sensor looks for both fast and slow burning fires.

Last update on 2020-08-13 PST - Details

There was a time when building codes required a dedicated smoke alarm and a dedicated carbon monoxide detector on every floor, along with other air monitors near sleeping areas and kitchens. Having both types of detectors housed in one unit makes this building code requirement much easier to satisfy. It also makes life a little less expensive for contractors and homeowners! Among our top five CO detector contenders, one unit stands out for its performance, interactivity, and aesthetics: The Nest Protect 2nd Gen Smoke + Carbon Monoxide Alarm.

Although the CO-monitoring aspect of the Nest Protect 2nd Gen Smoke + Carbon Monoxide Alarm appears to take a back seat to its smoke-detecting feature, users get the same level of protection against toxic carbon monoxide buildup as they do from fire. Most home CO detectors are designed to sample the air and record carbon monoxide levels over time. Long-term exposure to low levels of CO (in the 30 PPM or lower range) can be just as hazardous as short-term exposure to high levels of CO (450 PPM or more). The Nest Protect measures both long-term and short-term exposure. 

While other CO detectors have an average lifespan of five to seven years, the Nest Protect CO detector remains effective for up to 10 years. All-electric homes may not face the same risk of CO exposure as those that use fossil fuels such as natural gas or wood, but it is still a wise idea to have both smoke and CO detectors placed near sleeping areas and other enclosed spaces. 

We especially like the interactivity offered by the Nest Protect 2nd Gen Smoke + Carbon Monoxide Alarm, since many fires and CO buildups happen while occupants are away. If you are planning to build a new home, we suggest this high-quality hybrid detector. Simply put, the Nest Protect 2nd Gen Smoke + Carbon Monoxide Alarm is the Best of the Best.

Last update on 2020-08-13 PST - Details


First Alert Dual-Power Carbon Monoxide Detector Alarm | Plug-In with Battery Backup and Digital Display, CO615
2,357 Reviews
First Alert Dual-Power Carbon Monoxide Detector Alarm | Plug-In with Battery Backup and Digital Display, CO615
  • Keep your family safe with this digital display, plug in carbon monoxide alarm; It works with any standard outlet and also has a battery backup for continuous monitoring of Carbon Monoxide levels, even if there's a power failure
  • Features an advanced electrochemical carbon monoxide sensor; Peak level feature displays the highest concentration of carbon monoxide measured
  • A loud 85 decibel alarm sounds when Carbon Monoxide levels reach dangerous levels
  • To ensure complete protection make sure to place one on each level of your home and in each bedroom
  • 7 year limited warranty; Equipped with end of life signal chirp, so you know when it’s time to replace the unit for safety

Last update on 2020-08-13 PST - Details

A carbon monoxide detector is one safety device that homeowners should hope "dies" in peace. Even low levels of CO can cause flu-like symptoms, headaches, vision problems, vertigo, and respiratory distress. High levels of CO can cause severe oxygen deprivation in the bloodstream and death. While all of our contenders provide fast, accurate readings of the ambient air's CO levels, one stands out as an affordable and flexible alternative to expensive hardwired models. That model is the First Alert CO615 Dual Power Carbon Monoxide Plug-In Alarm.

Many building codes require (or suggest) at least one CO detector on each level of the home. Additional units should be placed near sleeping areas and other enclosed spaces where carbon monoxide could potentially accumulate. However, some homeowners and renters simply cannot afford to maintain and replace four or five high-end carbon monoxide detectors. One or two well-placed First Alert CO615 CO detectors, at a cost of apiece, can still provide peace of mind for users who want to make sure their homes are properly ventilated and their loved ones are safe from the hazards of carbon monoxide.

The First Alert CO615 can be plugged into any standard outlet, mounted on a wall with a six-foot power cord, or operated by two AA batteries. If one area of concern doesn't yield higher-than-average carbon monoxide readings, the entire unit can be easily removed and installed in another area. This flexibility saves lives. For this and many other reasons, we declare the First Alert CO615 Dual Power Carbon Monoxide Plug-In Alarm to be the Best Bang for Your Buck!

First Alert Dual-Power Carbon Monoxide Detector Alarm | Plug-In with Battery Backup and Digital Display, CO615
A loud 85 decibel alarm sounds when Carbon Monoxide levels reach dangerous levels; All first alert CO alarms are rigorously tested to meet UL standards
$59.99 −$30.00 $29.99

Last update on 2020-08-13 PST - Details

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