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You can’t see or smell deadly carbon monoxide. That makes a carbon monoxide detector an absolute must for homes with fuel-burning appliances of any kind. Carbon monoxide alarms generally fall into two categories: Those that can connect to smoke alarms and other carbon monoxide alarms, and units that work independently.
Independent units are usually the most inexpensive and easy to install, but you may need several for complete coverage. Interconnected units often function as smoke detectors as well—a nice bonus—and can trigger an alert on all of a home’s alarms. These may require a bit more installation know-how, especially if they're hard-wired instead of battery-operated.
What to Look for in a Carbon Monoxide Alarm
The first choice you’ll want to make is whether you want a product that’s both a smoke and carbon monoxide detector. If you already have smoke detectors in your house, it will probably be less expensive to simply buy supplementary CO alarms. However, if you’re in the market for both, you can cross two items off your to-do list with two-in-one units.
Do you want an alarm that’s plugged into an outlet, battery-powered, or hardwired? Battery-powered units can be placed anywhere, but you’ll have to stay on top of their battery status. Plug-in products won’t die on you, but you’re limited in where you can put them. Hardwired units, on the other hand, require more complex installation.
Many 2-in-1 CO and smoke detectors can be interconnected, meaning if an alarm goes off on the first floor of your home, it will trigger the alarms on the second floor as well. This ensures you won’t ever miss the alarm. Some can also be integrated with other smart home devices, like Alexa. However, if the alarm you choose can’t be interconnected, you will have to buy numerous units to cover your entire home.
Here, the best carbon monoxide alarms available today.
Best Overall: Kidde Nighthawk Plug-In AC/DC Carbon Monoxide Alarm Detector
Dimensions: 6.06 x 3.75 x 1.75-inches | Weight: 1.04 pounds | Sensor Type: Electrochemical | Power Source: Corded electric | Temperature Rating: 37.8 degrees Celsius
Easy-to-read digital display
Plug-in rather than digital
The reliable Kidde Nighthawk is a top pick for a carbon monoxide alarm. This plug-in model features a digital reading of current carbon monoxide levels (also referred to as CO) and it’s refreshed every 15 seconds. The unit includes a 9V battery backup for peace of mind and continued monitoring in the case of a power outage.
The easy-to-read digital display is front and center on this alarm. You'll appreciate being able to see the CO level at a glance, and this information could be very useful to first responders in the event of a leak. A button labeled ‘Peak Level’ makes it easy to recall the highest recorded level of CO since the alarm was last unplugged or reset.
You will need to give up an outlet to plug in this carbon monoxide alarm, but the peace of mind that the Kidde Nighthawk provides is well worth it. Additionally, the unit includes extra cord, so you can plug it into an outlet and set the unit on a nearby table, shelf, or counter.
An especially useful feature is the fact that the unit can be unplugged and carried into different rooms for an instant reading, thanks to the onboard battery backup. The Kidde Nighthawk is a reliable, useful carbon monoxide alarm that can keep you protected.
"After ten years, the Nighthawk’s end of life alarm will sound repeatedly to let you know it’s time to replace the whole unit. That really gave us some peace of mind."—Stacey L. Nash, Product Tester
Runner-Up Best Overall: FIRST ALERT Battery Operated Combination Smoke and Carbon Monoxide Alarm
Dimensions: 5 x 5 x 2-inches | Weight: 3.2 ounces | Sensor Type: Photoelectric | Power Source: Battery-powered | Temperature Rating: Varies
Equipped with a wireless safety network
No option to personalize locations
These carbon monoxide detectors also pull double duty as smoke alarms. But one of the favorite features of the First Alert Combination Alarm is the unit’s voice location function.
During set-up, program the unit for the room it’s located in—child’s bedroom, living room, guest room, etc.—for immediate identification of where the alarm is originating from. There are 11 pre-recorded locations to choose from, but no option to personalize the locations (such as: ‘Matt’s Bedroom’ or ‘Downstairs Guest Room’). These alarms are also equipped with a wireless safety network, meaning that up to 18 units can be connected within the home. When one alarm is activated, all connected units will sound the warning—including the voice alarm of which room has the problem.
Since these units are battery-operated and not hardwired, they’re easy to install in any location regardless of existing wiring. When the battery is low, all connected units will sound the warning and tell you which room contains the low battery. The most notable drawback is the lack of a digital CO reading, but these two-in-one smoke and carbon monoxide alarms are popular for their voice location function and easy installation.
Best High-End: Google Nest Protect 2nd Generation
Dimensions: 5.3 x 1.5 x 5.3-inches | Weight: 1-pound | Sensor Type: Split-spectrum | Power Source: Battery | Temperature Rating: Varies
Can be battery operated or have hardwired installation
Boasts convenient features
More expensive than other units
For a full-featured carbon monoxide alarm, look no further than the Nest Protect Smoke & Carbon Monoxide Alarm. This dual-purpose unit monitors for both carbon monoxide and smoke. An easy-to-use app makes it easy to keep tabs on the system, and provides additional notifications if problems are encountered.
The Nest Protect can be ordered for either hardwired installation or battery operation. No matter which model you choose, the unit is enabled with Wi-Fi and provides instant updates to your phone if a problem is encountered or battery life is low. You can also test the alarm from your phone and receive a full report when the test is complete. But you don’t have to worry if you forget to initiate a test since the unit tests itself over 400 times a day.
This high-end carbon monoxide alarm links to other units installed in your home and is also compatible with products in the Google Nest family. It also is popular for its voice function—if the alarm is triggered, the unit will tell you which room is experiencing a problem.
"For a web-enabled device, the Nest Protect’s setup is paint by numbers—especially if you go with the battery mode."—Nathan Borchelt, Product Tester
Best Budget: Kidde Carbon Monoxide Detector Alarm
Dimensions: 3 x 7 x 11-inches | Weight: 0.5-pounds | Sensor Type: Detector | Power Source: Battery-powered | Temperature Rating: Varies
Operates on two AA batteries
Features LED lights
Not as long-lasting as other units
You can’t put a price on safety, but this basic model of carbon monoxide alarm from Kidde offers reliable performance at a great value. The Kidde Carbon Monoxide Alarm (model 21025778) operates using two AA batteries and can be placed in any room.
This budget carbon monoxide alarm is simple but covers all the bases. An 85-decibel alarm will alert you if dangerous levels of carbon monoxide are detected. LED lights will provide visual confirmation if the alarm is triggered, and a Test/Reset button allows you to confirm that the unit is working.
While some people prefer a carbon monoxide detector that can be plugged in, others like the battery power of this unit.
Best for Long Battery Life: FIRST ALERT Carbon Monoxide Detector
Dimensions: 0.94 x 4.75 x 2.63-inches | Weight: 6.7 ounces | Sensor Type: Electrochemical | Power Source: Battery-powered | Temperature Rating: Varies
Built-in lithium-ion battery
Sealed carbon monoxide detector
Long battery life
More expensive than other units
If you don’t have a hardwired carbon monoxide alarm and don’t want the hassle of routinely changing batteries, then consider a model with a built-in lithium-ion battery. The First Alert Carbon Monoxide Detector with 10-Year Battery (model CO710) is a popular pick for its long life and an easy-to-read display.
This is a sealed carbon monoxide detector, meaning you won’t be able to open the unit to change the battery. But fortunately, you won’t need to—since the included lithium-ion battery will last the life of the unit. Most safety regulations require that carbon monoxide detectors be replaced at least every 10 years, and in some cases, even more frequently.
With a long battery life, this carbon monoxide alarm will never wake you up in the middle of the night with the dreaded ‘low battery alarm.’ However, when the unit is approaching the end of its 10-year lifespan, it will sound an alert to let you know it’s time to replace it. You'll also appreciate the fact that a digital display provides an indicator of CO concentration, peak CO levels, and the current temperature in the room.
Best Smart Home: FIRST ALERT Alexa Enabled Smoke Detector and Carbon Monoxide Detector Alarm
Dimensions: 7 x 7 x 2-inches | Weight: 1.76 pounds | Sensor Type: Photoelectric | Power Source: Battery-powered | Temperature Rating: Varies
Features a premium home speaker
Integrated with an app for smart devices
More expensive than other units
For a safer smart home, install the OneLink Safe and Sound Carbon Monoxide Alarm. This two-in-one device makes no compromises and is a great carbon monoxide detector for your smart home.
The OneLink is equipped to detect both smoke and carbon monoxide. However, the unit also features a premium home speaker that is Alexa-enabled. You can play favorite tunes, ask Alexa about the weather, and more with this carbon monoxide detector.
The device is also integrated with an app for your smart devices. Using the app, you can receive alerts, track CO levels, and adjust the nightlight function of the unit. This unit operates on AC power but includes adaptor plugs that utilize existing hardwired connections.
While this is a pricier carbon monoxide detector, but it offers multi-functionality that is perfect for your smart home.
Best Portable: FORENSICS Car, Vehicle, Aircraft Carbon Monoxide CO Detector
Dimensions: 2.7 x 1.9 x 0.8-inches | Weight: 2 ounces | Sensor Type: N/A | Power Source: Battery-powered | Temperature Rating: Varies
Provides current reading of CO levels
Weighs only 2 ounces
Only has a 1-year battery life
For a portable carbon monoxide alarm to keep you protected even on the go, the Forensics Car and Aircraft Carbon Monoxide Detector has you covered. This sleek and small model weighs only 2 ounces but has a digital display and a handful of useful features.
This portable carbon monoxide alarm detects the presence of this gas at levels as low as 9ppm. If the gas is present for 60 seconds or more, an alarm will sound. Most household carbon monoxide detectors won’t sound an alert until levels approach 70ppm for 60 minutes or more. If you’re operating a vehicle, significantly lower levels of carbon monoxide can cause drowsiness and potentially impair your ability to safely drive. The Forensics Car and Aircraft Carbon Monoxide Detector provides early warning of CO levels and is a smart addition for your car, airplane, or travel kit.
The battery life is rated for up to a year, and an indicator of remaining battery life is included in the digital display. You can also check the current reading of CO levels on the display, or quick press the power button to see the max reading of CO detected by the unit since the last reset. People have used these portable carbon monoxide detectors extensively in personal vehicles, fleet vehicles, airplanes, and on trips for peace of mind and safety.
Best Multi-Pack: Kidde Code One Battery Operated Carbon Monoxide Detector
Dimensions: 1.5 x 4.5 x 2.75-inches | Weight: 10.4 ounces | Sensor Type: N/A | Power Source: Battery-powered | Temperature Rating: Varies
Includes multiple units
Battery-operated as opposed to plug-in
Since carbon monoxide alarms are limited in their detection radius, it often makes sense to have several units in operation in your home. The size of each room and overall layout will dictate how many carbon monoxide monitors you need, but the Kidde Code One Multi-Pack makes it easy to protect your whole house.
This carbon monoxide alarm multi-pack includes six battery-operated units. Instead of worrying about hardwiring or taking up outlet space, this model is easy to set up and move around. Three AA batteries give you about six months of power, and the unit itself has a 7-year life span. If you have a large house, manage rental properties, or need to keep back-up detectors at the ready, consider this multi-pack of carbon monoxide detectors.
Our top pick is the Kidde Nighthawk Carbon Monoxide Detector, a reliable alarm that's easy to set up and has three mounting options for added flexibility. If you're looking for a smart home-compatible option, check out the Google Nest Protect Smoke and Carbon Monoxide Alarm. It has plenty of smart features, including auto-testing and automatic battery monitoring.
Why Trust The Spruce?
This article was written by Erica Puisis, a freelance writer who has contributed to The Spruce since 2017. She specializes in interior design and has experience covering everything from appliances to smart home products. To make this list, she considered each device's price and size as well as interconnectivity, smoke detection, and installation.