A carbon monoxide alarm is considered a home safety necessity. The device is tuned to detect dangerous levels of carbon monoxide, which is vital because carbon monoxide is colorless, odorless, and can be lethal.
“Carbon monoxide is known as a 'silent' killer because humans are unable to see, smell, or taste it,” says Dr. Kelly Johnson-Arbor, the Interim Executive Director of the National Capital Poison Center and a medical toxicologist. She points out that a working carbon monoxide detector emits a loud, obnoxious noise in the presence of dangerous levels of carbon monoxide: “The noise is loud enough to wake up a sleeping individual who might otherwise not experience any warning signs of carbon monoxide poisoning.”
We researched the best options available for carbon monoxide alarms, including hardwired, plug-in, and battery-powered options.
Kidde Nighthawk Plug-In AC/DC Carbon Monoxide Alarm Detector
Digital display with CO PPM
Can recall past peak CO levels
Alarm not as forceful as expected
Lacks smoke detector sensor
The Kidde Nighthawk has one purpose: to monitor for dangerous levels of carbon monoxide. It doesn’t include a smoke detector function, which was our biggest point of concern. However, it’s an ideal choice if you’re specifically looking for a carbon monoxide alarm and already have hardwired smoke detectors in your home. We found it easy to use and reliable, earning it our top recommendation for a carbon monoxide alarm.
This plug-in model requires no electrical know-how and takes up just one standard outlet. Once it powers on for the first time, it lasts 10 years before signaling it's time for a replacement. A 9-volt battery backup gives you confidence that the Kidde Nighthawk keeps monitoring for carbon monoxide, even if there is a power outage. The Kidde Nighthawk also stands out for having a simple interface. It has just two buttons: for testing the unit and to recall peak levels of detected carbon monoxide (CO), measured in parts per million (PPM).
The digital display is a helpful feature not always found on carbon monoxide detectors. It provides a reading of current CO levels and is helpful for interpreting the beeps that the device may emit. The intermittent pattern of the alarm—four beeps, followed by 5 seconds of silence—may not immediately grab your attention. However, it is loud enough that we feel confident it would wake most people while sleeping. We found that the volume gets your attention. When we tested, there were children in another room who were on high alert once the alarm started sounding.
Dr. Johnson-Arbor suggests that carbon monoxide detectors should always be placed in or within 10 feet of any sleeping area. With this parameter in mind, the Kidde Nighthawk is an excellent choice.
Price at time of publish: $34
Dimensions: 6.06 x 3.75 x 1.75 inches | Power Source: Plug-in, with 9-volt battery backup | Smoke Detector: No | Warranty: 10 years
First Alert CO400 Battery-Operated Carbon Monoxide Detector
Flexible placement options
85-decibel audio alarm
Simple design that's easy to monitor
Only rated for 5 years of use
A budget carbon monoxide alarm is a small investment towards peace of mind. For under $25, a basic model, like the First Alert CO400, continuously monitors for harmful levels of carbon monoxide and sounds the alarm if such a condition develops. Besides the audible 85-decibel alarm, a flashing LED also provides a visual indicator of danger.
The First Alert Battery-Operated Carbon Monoxide Detector uses a proven form of detection in the form of an electrochemical sensor. The unit is powered only by a 9-volt battery, so you’re not limited on where to place the carbon monoxide detector because of outlet proximity or electrical wire connections. While this product represents a good value, it’s worth noting that it should be replaced every 5 years, while some other models offer a 10-year life expectancy. An end-of-life signal chirp and low-battery beep round out the features of this simple unit.
Price at time of publish: $42
Dimensions: 3.4 x 1.5 x 5 inches | Power Source: 9-volt battery | Smoke Detector: No | Warranty: 5 years
Kidde KN-COB-DP2 Carbon Monoxide Detector, AC Plug-In
Compact for easy placement
10-year life span
Uses 2 AA batteries for backup
No digital display
Difficult-to-interpret indicator lights
A plug-in carbon monoxide alarm offers a simple solution to protecting yourself against harmful levels of this poisonous gas. The Kidde KN-COB-DP2 Carbon Monoxide Detector is fast to install—just plug it into a standard electrical outlet. This model has a 10-year life span that surpasses the 5- or 7-year life expectancy of some other plug-in carbon monoxide detectors.
Like most similar products, this Kidde model includes a battery backup for uninterrupted monitoring, even if the power supply is interrupted. It requires two AA batteries, which you may be more likely to have on hand than the 9-volt battery backup some other plug-in carbon monoxide detectors require.
Whether the unit is running on electricity or battery power, an 85-decibel alarm sounds if it detects carbon monoxide levels exceeding safe levels. This basic model lacks a digital display, so you need to consult the owner’s manual to learn what the small color-coded light signals mean. The light glows green during normal operation but turns red because of an alarm, low battery power, or the end of the unit’s life span.
Price at time of publish: $30
Dimensions: 2.75 x 1.5 x 4.5 inches | Power Source: Plug-in, with AA battery backup | Smoke Detector: No | | Warranty: 10 years
Google Nest Protect Smoke & CO Alarm 2nd Generation
Battery power or hardwired
Tonal and verbal alarms
Monitors battery level and self-tests
Attractive aesthetic design
Only 2-year warranty
Requires 6 AA batteries
A smart carbon monoxide detector integrates with your existing smart home setup to keep you informed and protected. Google’s popular Nest smart home ecosystem offers an easy-to-use carbon monoxide detector that monitors for dangerous levels while staying alert to smoke from smoldering fires or flames. It’s intelligent enough to alert you to low levels of smoke (such as from high-heat cooking) without blasting the alarm. You can silence the Nest Protect alarms within the app, giving you convenience and control on your smartphone.
There are plenty more user-friendly features built into this smoke and carbon monoxide detector that integrates with Google Assistant, but the safety benefits are the most important. While virtually all carbon monoxide detectors include a testing function, it’s easy to skip out on actually performing a test to ensure that your unit is operating properly. The Nest Protect is designed to silently test its batteries and sensors more than 400 times each day. Once a month, it tests the audible alarm functions by sounding the speaker and horn within the unit. Before bed each night, you see the light ring around the center of the unit turn green to indicate that the battery level is sufficient and assure you won’t be woken up to an unpleasant low-battery alarm. If smoke or carbon monoxide levels become dangerous, the device alternates between an audible alarm and a voice alert specifying where the problem originates from. The center ring of the Nest Protect also glows red to give you a visual indicator there is an emergency.
Nest Protect is available as a battery-operated or hardwired unit. We prefer the hardwire option because all the features and functions of this smart carbon monoxide detector can drain battery power. So it’s not surprising that the battery version requires 6 AA cells. (The hardwired version needs 3 AA batteries for its backup power system.)
The sensors inside this combo smoke and carbon monoxide detector have a 10-year life span, which is good to know if you’re installing the unit in a state that regulates the life expectancy of smoke detectors. However, it’s worth noting that the manufacturer’s warranty on the unit is only valid for 2 years.
Price at time of publish: $120
Dimensions: 6.22 x 2.76 x 6.26 inches | Power Source: Battery or hard-wired | Smoke Detector: Yes | Warranty: 2 years
Kidde Battery-Powered Carbon Monoxide Detector
Easy-access battery compartment
Tabletop or wall-mount installation
Audible alarm and LED flashing light
No digital display
A compact carbon monoxide alarm saves space and is easy to take along as a portable monitor. We recommend the battery-operated (two AA cells) Kidde KN-COB-B-LPM, which fits in the palm of your hand. It doesn't take up much space on a tabletop. Or you can install it on a wall, as long as there is space for its 4.5 x 2.75 x 1.5-inch footprint.
Despite the compact size, this carbon monoxide detector is equipped with a standard 85-decibel alarm that is plenty loud enough to alert you if elevated levels of CO are present. In addition, a flashing LED light gives a visual heads-up that the unit is operating as expected (green light) or if an alarm is active (red light). There are few other features to note on this basic device, but it operates in a straightforward manner and has a 10-year life span.
Price at time of publish: $28
Dimensions: 4.5 x 2.75 x 1.5 inches | Power Source: 2 AA batteries | Smoke Detector: No | Warranty: 10 years
First Alert BRK CO5120BN Hardwired Carbon Monoxide Detector
Battery backup to ensure monitoring
Easy to install
Integrates with First Alert devices
Lacks smoke and fire sensors
Audio alerts only
A hardwired carbon monoxide alarm integrates into your home’s electrical system, freeing up an outlet and eliminating frequent battery replacement. The First Alert CO5120BN is a basic mounted carbon monoxide detector that we recommend because it can connect with up to 18 other First Alert devices and it includes a 9-volt battery back-up. Both are important safety considerations that ensure you're notified if carbon monoxide reaches dangerous levels.
The First Alert CO5120BN's electrochemical sensor detects carbon monoxide levels over 30 parts per million. (Symptoms become more noticeable over 70 ppm.) When the concentration exceeds safety thresholds, it triggers an 85-decibel alarm. The only other warning is a small red light, which flashes in a special pattern when the detector is triggered. The light keeps flashing, even when CO drops below hazard levels. So you need to manually clear the latching alarm by testing the unit.
Price at time of publish: $35
Dimensions: 5.53 x 2.09 x 5.72 inches | Power Source: Hardwired, 9-volt battery backup | Smoke Detector: No | Warranty: 10 years
Best with Smoke Alarm
Kidde Battery-Operated Combination Smoke/Carbon Monoxide Alarm with Voice Warning
Voices alarm type
Smart Hush silences fire alarms
Connectable to other Kidde devices
Lacks photoelectric fire sensor
No smart features
A combination carbon monoxide detector can efficiently protect your home and family from harmful gas leaks and alert you to fire danger. The Kidde Smoke & Carbon Monoxide Detector is about the same size as your average smoke detector, but includes an electrochemical sensor to detect carbon monoxide. If an alarm is triggered, this model clearly announces: “Warning carbon monoxide” or “Fire.” If a low-battery alarm is initiated, the voice announcement makes that clear as well.
This combo smoke and carbon monoxide detector uses 2 AA batteries. It’s rated for 10 years of use, making it compliant even in states that require a 10-year lifespan for smoke detectors. It’s also worth noting that the Kidde Smoke & Carbon Monoxide Detector uses an ionization sensor, which is likely to register a fast-burning fire more quickly than a product using a photoelectric sensor to detect flaming and smoldering fires. During our in-home testing, we accidentally set off the smoke alarm while cooking, but the Smart Hush feature on this device will silence the alarm for 8 minutes if this happens to you, giving you time to clear the smoke from the kitchen or from an extinguished candle.
Price at time of publish: $45
Dimensions: 5.6 x 5.6 x 1.8 inches | Power Source: 2 AA batteries | Smoke Detector: Yes | Warranty: 10 year
Best Digital Display
X-Sense XC01-R Carbon Monoxide Detector
Displays CO in parts per million
Recalls of highest detected levels
Compact and portable design
Not suitable for extreme temps
The most basic carbon monoxide detectors may get the job done by using loud, audible alarms to indicate the presence of high levels of this gas. However, a carbon monoxide detector with a digital display, like this portable model from X-Sense, can provide you with more information and monitoring data. While the display information is handy, rest assured the 85-decibel alarm still alerts you audibly if high levels of carbon monoxide are detected.
However, we recommend this compact carbon monoxide detector for the information it provides, via an easy-to-read LCD screen. It displays detected CO in parts per million (PPM), along with a battery status indicator, so you’re not caught by surprise when the battery power runs low. Fortunately, the 5-year lithium-ion battery offers long life and shouldn't require frequent replacement during the unit's expected 10-year life span.
A handy feature is the Peak CO Concentration Memory. Press this button and the display shows you the highest detected levels of carbon monoxide. Also enhancing the visual cues, a color-coded LCD status bar sits just below the digital display.
As a portable carbon monoxide alarm, keep in mind that this unit is functional only in ambient air temperatures from 40 and 100 degrees Fahrenheit. While that’s unlikely to be a problem in your house, it may not be functional if deployed in a garage, shed, or other unheated or uncooled structure.
Price at time of publish: $40
Dimensions: 5.3 x 2.5 x 0.6 inches | Power Source: Battery | Smoke Detector: No | Alerts: Both | Warranty: 5 years
First Alert Carbon Monoxide Detector
Digital display includes temperature
Li-ion battery lasts the life of the unit
Peak CO level recall function
No install needed
Battery not replaceable
If you’re looking for a carbon monoxide detector with versatile placement options, consider a battery-powered unit. The First Alert CO710 Carbon Monoxide Detector doesn’t need to be hardwired to your home’s electrical system or plugged into an outlet. Instead, it operates on power supplied by a long-lasting lithium-ion battery. This makes it a good pick if you’re looking for a portable carbon monoxide alarm for use while traveling.
Many battery-powered carbon monoxide alarms operate using AA or 9-volt batteries that require occasional replacement. However, this popular model from First Alert comes equipped with a lithium-ion battery that is designed to last for the 10-year life span of the unit. The long-lasting battery ensures that the carbon monoxide detector stays on alert at all times, as well as powers the digital display.
Some display features worth noting include that it displays CO in parts per million, along with a graphical rendition of the relative concentration level. A peak CO memory function also notifies you of the highest detected levels. It even includes an ambient temperature reading which, frankly, adds no functionality but is nice to have.
Price at time of publish: $29
Dimensions: 4.75 x 2.63 x 0.94 inches | Power Source: Lithium-ion battery | Smoke Detector: No | Warranty: 10 years
First Alert Onelink Safe & Sound
Bluetooth speaker and lighting
Smart home Alexa integration
Sends alerts to your smartphone
Costs more than other models
The First Alert OneLink Safe & Sound is a carbon monoxide detector that also detects smoke. Its smart features include integration with Amazon Alexa and Apple HomeKit, giving you voice control over convenient built-in functions such as a Bluetooth speaker and integrated pathway lighting. The product's 10-year life span makes it one of the priciest carbon monoxide detectors on the market. Still, it’s a worthwhile choice if you want a smart device that also offers voice-control for your music and smart home.
The concept behind the First Alert OneLink Safe & Sound is to combine functional benefits with consistent monitoring of carbon monoxide and smoke levels. The voice-controlled carbon monoxide detector belts out music or podcasts from its speaker, using a Bluetooth connection to your smart device. You can tell Alexa to start or stop playing audio, or use the hands-free technology to control other aspects of your smart home. You also can customize the intensity and color of the built-in light—a handy night light for hallways and other areas.
A smart function that's safety-related is this model’s ability to send an alert to your smartphone if it detects a threat from carbon monoxide or smoke. This means you have an instant heads up wherever you are—in the backyard, at the office, or away on vacation, when a potentially dangerous situation has developed at home.
Price at time of publish: $278
Dimensions: 6.8 x 6.8 x 2.26 inches | Power Source: Hardwired, lithium-ion battery backup | Smoke Detector: Yes | Alerts: Both | Warranty: 10 years
Gentex CO1209 Hardwired Interconnect CO Alarm
Connects to other Gentex devices
Noted for very reliable performance
Requires replacement every 5 years
Pricier than similar models
Installing multiple carbon monoxide detectors is a wise choice, especially in large homes or if you have multiple sources of potential gas leakage such as a dryer vent and gas hot water heater. By choosing an interconnected carbon monoxide alarm, you can monitor for the presence of this deadly gas and hear an alarm from all devices, even if only one device detects CO. The Gentex CO1209 carbon monoxide alarm, designed for residential or commercial settings, has a basic, utilitarian design that makes testing and monitoring the unit simple. Also, its tamper-resistant design makes it a good choice for rental properties.
This hardwired carbon monoxide detector can interconnect with other Gentex devices equipped with the brand’s Dualink technology. In the event of a power outage, it remains operational with the help of a 9-volt battery backup. A self-test button on the front of the unit ensures that it’s working properly. It only has a 5-year lifespan, so you have to replace the unit more often than similar products. But it has a reputation for offering reliable performance with few false alarms.
Price at time of publish: $40
Dimensions: 6.25 x 6.25 x 1.8 inches | Power Source: Hardwired | Smoke Detector: No | Warranty: 1 year
We recommend the Kidde Nighthawk Carbon Monoxide Detector because it's easy to install and use, thanks to the plug-in design and digital display. A battery backup also ensures that this carbon monoxide alarm stays on alert even when the power is out. Of course there are even more advanced carbon monoxide detectors on the market, so if you're looking for a smart home option, then the Google Nest Protect Smoke Alarm, Detector, and Carbon Monoxide Detector is an obvious choice. This high-end option alerts you to your smart device in the event of elevated levels of carbon monoxide or smoke, and also uses a voice alarm to provide a clear, audible warning of danger. It's a great pick if you want to monitor the safety of your home while you're away at the office, running errands, or on vacation.
What to Look For in a Carbon Monoxide Detector
The type of carbon monoxide detector you select depends on your monitoring needs. If you have installed smoke detectors, then a unit specifically designed to detect only carbon monoxide may be all you need. However, if you’re looking for a unit that detects smoke and carbon monoxide, or if you live in a state that requires both types of devices by law, then installing a combination device is an efficient way to meet safety and legal requirements.
The power source of a carbon monoxide detector dictates its placement options and how easy it is to install. A hardwired carbon monoxide alarm ties into your home’s electrical grid but uses a battery backup in the event of a power failure. This is the most advanced type of carbon monoxide detector to install, especially if you don’t have an existing hardwired connection.
Carbon monoxide detectors with plug-in or battery power sources are the easiest to install. Plug-in models like this Kidde Carbon Monoxide Detector draw power from standard electrical outlets. Like hardwired carbon monoxide detectors, they usually install batteries as alternative power sources.
Battery-only carbon monoxide detectors are also sometimes referred to as portable models. The First Alert CO400 Carbon Monoxide Detector is ideal for travel or use in a room where installation or plug-in of a carbon monoxide detector installation or plug-in isn’t feasible.
Many carbon monoxide detectors have no display. However, most units have small lights that glow or blink steadily to indicate normal operation, an error, or an alarm. If you want more information from a carbon monoxide detector, you can search out a model with a display that gives you a reading of carbon monoxide levels in parts per million, display highest recorded levels or carbon monoxide, give you battery life status updates, and even indicate the room air temperature. The First Alert CO710 Carbon Monoxide Detector has a digital screen that displays the current temperature, as well as the average and maximum CO levels in the room.
Interconnectivity refers to a carbon monoxide detector's ability to connect to other home safety monitoring devices such as other CO detectors or smoke detectors. All interconnected carbon monoxide detectors sound when one device detects dangerous CO levels. Interconnectivity of carbon monoxide detectors is a legal requirement in some states.
When shopping for interconnected carbon monoxide detectors, keep in mind that compatibility is not universal among all devices across all brands. Check the requirements for any existing carbon monoxide or smoke detectors you have installed; then look for carbon monoxide alarms with compatible interconnectivity. You should also look for devices that have latching alarms. They indicate which carbon monoxide detector set off the alarm, which can be helpful in finding the source of a CO leak.
Sensors and Sensitivity
Carbon monoxide detectors use electrochemical sensors to detect the presence of the colorless, odorless gas. A carbon monoxide detector's sensitivity should align with Underwriter’s Laboratory (UL) safety standards. These specify that a carbon monoxide detector should alert you within 15 minutes if CO levels reach 400 PPM; within 35 minutes if CO levels reach 200 PPM; and within 90 minutes for CO levels that reach 100 PPM.
A carbon monoxide alarm sensor can become damaged by particles in the air. For this reason, Dr. Kelly Johnson-Arbor, the Interim Executive Director of the National Capital Poison Center and a medical toxicologist, provides the following caution: “Carbon monoxide detectors should not be installed in furnace rooms, as the detector's sensor can be clogged or damaged by microscopic particles emitted from the furnace.”
Carbon monoxide detectors are equipped with audible alarms that sound at a volume of 85 decibels. However some models also include voice alarms. These function depending on the device, but they may announce the danger or specify the location where the threat was detected.
How often should you replace a carbon monoxide detector?
Generally, carbon monoxide detectors have life spans of 5 to 10 years. When the detector is at or near the end of its life, it typically emits an alarm. To differentiate between an end-of-life detector alarm and an actual carbon monoxide alarm, look on the product for guidance or check the packaging for details on how these alarms differ. (The end-of-life alarm is often a series of slow beeps that occur every few minutes.) Dr. Johnson-Arbor also offers this tip: “Carbon monoxide detectors frequently have a space on them where you can label them with the date of purchase, so that you can remember to replace them at the end of their life span.”
Where should you place carbon monoxide detectors?
Carbon monoxide detectors should be placed near potential sources of the gas such as a dryer vent or water heater. It’s also very important to have them near sleeping areas, according to Dr. Johnson-Arbor. “Carbon monoxide detectors should be installed in every sleeping area of a house," she says. "If you sleep in a bedroom, a carbon monoxide detector should be present in or within 10 feet of the bedroom. If you sleep in a basement, you should have a carbon monoxide detector in the basement where you sleep.”
Do you need a carbon monoxide detector in every room?
It’s generally not necessary to put a carbon monoxide detector in every room, but the Environmental Protection Agency (EPA) states that at least one device should be installed on every floor of your home. You should also have a carbon monoxide alarm installed in close proximity to every sleeping area, which may mean having more than one device installed on a particular floor of your house.
What generates carbon monoxide in a house?
Carbon monoxide is a naturally occuring gas that becomes harmful at concentrated levels. “Anything that burns carbon-based fuel, whether it's a gas grill, a charcoal grill, a propane-powered generator, or a wood burning fireplace, will generate carbon monoxide,” according to Dr. Johnson-Arbor. “The only appliances that do not generate carbon monoxide are electric powered devices.”
Many appliances that burn fuel, including water heaters, furnaces, and dryers, pose no threat when operating normally. But they may leak carbon monoxide if their vent or exhaust systems become blocked. It’s important to regularly maintain and monitor those appliances and install carbon monoxide detectors nearby to warn if a leak is detected.
Why Trust The Spruce?
This article was researched and written by Erica Puisis, a freelance writer specializing in home products and appliances. When researching picks for this list, she compared various types of carbon monoxide alarms, including options with and without smoke detection. She evaluated the most popular models based on the power source, display options, and any additional safety or smart home functions.
As part of the research process, Puisis also interviewed Dr. Kelly Johnson-Arbor, Co-Medical Director and Interim Executive Director of the National Capital Poison Center. Dr. Johnson-Arbor shared information regarding the importance of having and installing carbon monoxide detectors in the home.