High Tech

Best Carbon Monoxide Detector for 2023

$34 at Amazon


First Alert CO615

Best carbon monoxide detector overall

$20 at Amazon


First Alert CO400

Best carbon monoxide detector on a budget

$151 at Walmart


First Alert Onelink 1042136 Battery Powered Smoke and Carbon Monoxide Detector

Best smoke and carbon monoxide combo detector

Carbon monoxide (CO) is a colorless, odorless gas that can be extremely dangerous to human health. It is produced by the incomplete combustion of fuels such as gasoline, oil, wood, propane and natural gas, and it can build up in enclosed spaces such as homes, garages, and basements.

Carbon monoxide is a threat because it displaces oxygen. When humans breathe in carbon monoxide, it binds to the hemoglobin in their red blood cells, replacing and reducing the amount of oxygen that can be carried by the blood. This can lead to a range of symptoms, from headaches and dizziness to confusion, nausea, and even death.

Having a carbon monoxide detector in your home can alert you to the presence of dangerous levels of CO and give you time to evacuate and seek medical attention if necessary. This is especially important because, as you may know, CO is often referred to as the “silent killer” due to its lack of odor or taste. To help you make the right decision, we gathered seven of the most popular carbon monoxide detectors and evaluated their ability to detect carbon monoxide at two hazardous concentration levels, 250 and 400 ppm (parts per million). Here are our picks:

Gianmarco Chumbe/CNET

At an average retail price right around $35, the CO615 from First Alert is the perfect carbon monoxide alarm if you’re looking for handy features and decent performance at an affordable price. 

Highlights include a digital display that shows real-time carbon monoxide concentration in ppm and battery level, a test/silence button for weekly testing and a peak CO level button to show the highest carbon monoxide concentration detected. This is a plug-in model that is backed-up by two AA batteries (Energizer E91 only). Just pick any outlet that is not controlled by a switch or dimmer, and that is at least 5 feet away from any fuel-burning appliance. Plug it and you’re ready to go. The unit can be hung in the wall with two screws and its cord extends at least 6 feet, giving you a little flexibility as far as where exactly you can install it in your home.

This unit ranked third in our quickness of response test. In average, it took a little more than 12 minutes to detect the presence of CO at 250ppm and just over 8 minutes to detect CO at 400ppm. The real-time CO reading is pretty accurate, taking only two minutes and a half to catch up to the reading shown in our control device. The CO reading on the detector went a little above what our control was showing. However, the discrepancy between the two readings remained below 7%. 

Having a real-time display of the CO concentration is incredibly useful. Most common CO alarms are designed to go off after the CO levels in an area have been above a certain threshold for a while. Having immediate and accurate access to this information can help you take swift preventive action before the alarm has a chance to react. 

Gianmarco Chumbe/CNET

If all you need is a carbon monoxide alarm that can reliably watch your back without leaving a hole in your pocket, then the First Alert CO400 is perfect for the task. 
Basic features include a single test/silence button and a very loud alarm. It doesn’t come with a digital display or any smart features, but it makes up what it lacks in fancy looks with performance and affordability. Typically available for $25 or less, the CO400 was the least expensive CO detector we tested, and it was also the fastest at detecting carbon monoxide at both concentration levels. At 250 ppm, its alarm was set off after an average of 10 minutes and 46 seconds and at 400 ppm, it only took 7 minutes and 3 seconds. Those are excellent results, regardless of price.

With its low asking price, the CO400 would also be a particularly good pick for multi-storied homes, where you should aim to have at least one detector on every floor. Plus, as a battery-powered model, it won’t add to your energy bill while remaining immune to power outages.  


Some units have the ability to detect both carbon monoxide molecules and smoke particles. These are called “combo” or “two in one” units. The First Alert Onelink 1042136 stood out in this category. 

This device got second place in our quickness of response test, detecting CO at 250 ppm after only 11 minutes and 42 seconds and, similarly, CO at 400 ppm after 8 minutes and 10 seconds. 

Despite not having a digital display, the voice alarm will speak to you in English and clearly state the current carbon monoxide concentration. Depending on where you installed your device, it can also tell you the exact location of the emergency. For example, during testing, you could hear the device saying: “Evacuate, evacuate. There’s carbon monoxide in the living room, 265 ppm.” To my surprise, the control device reading for this round was 260 ppm. That amounts to an accuracy error of less than 2%, which is significantly better than anything else we tested. 

Additionally, the Onelink is a compelling option for those seeking smart functionality. It’s compatible with Google, Apple HomeKit and Alexa. All you have to do is download the Onelink Home app and create a free account. Then, follow the instructions to set up a new device. From the app, you can test/silence your carbon monoxide alarm, interconnect other carbon monoxide detectors in your home and get emergency notifications to your smartphone.

All of that said, there are two caveats worth mentioning here. First is the cost. Often selling for more than $100, the Onelink combo detector is an expensive option, particularly if you’re shopping for more than one in something like a multi-story home. On top of that, while it performed well in our CO tests, it was less impressive when we tested its smoke detection capabilities, taking over a minute to detect a controlled, slow-smoldering fire nearby. While not disqualifying, that was still almost twice as long as it took other combo detectors to react.

How we test carbon monoxide detectors

To put these detectors to the test, we took to the lab and built a test rig designed to measure each unit’s response time to varying concentrations of carbon monoxide, specifically at 250 ppm and 400 ppm. Our goal was to determine each detector’s respective effectiveness at detecting potentially hazardous levels of carbon monoxide. To declare our winners, we also took into account features that add to the overall user experience, performance and cost-efficiency of each unit.

For the 250 ppm concentration level, we try to simulate a situation where carbon monoxide has begun to build up to hazardous levels. We test twice at this concentration and average the results. At 400 ppm, we replicate a worst-case-scenario, a potentially deadly situation, and give the units a pass or fail score. Spoiler alert: they will all save your life, which goes to show how important it is to have a carbon monoxide detector installed in every floor of your home.  

CNET's test rig for carbon monoxide detectors pumps the hazardous gas directly into an enclosed test chamber, where we can measure each detector's effectiveness at quickly sounding an alarm at various CO thresholds.

Our custom-built carbon monoxide detector test station. It’s one of the deadliest things we’ve ever put together in our product testing lab.

Gianmarco Chumbe/CNET

This is one of the most dangerous tests we’ve ever conducted. Carbon monoxide exposure is no joke. It’s virtually undetectable and, well, quite deadly. We needed to create a safe way of testing carbon monoxide detectors without risking the health and safety of our laboratory staff. So, I made use of my rudimentary carpentry skills and built a CO detector test station. Its components are:

  • CO detector chamber — made using wood, plexiglass, silicon, tape and a bunch of finish nails 
  • CO tank with gas flow regulator — cylinder tank containing CO at 2500 ppm and balance air
  • Testo 300 with CO Ambient sensor — our control device for this experiment
  • Two portable CO gas alarms

A look at the interior of CNET's carbon monoxide detector test rig. It's a sealed enclosure made of wood and plexiglass that features an intake for CO to enter, a controlled CO detector, and the specific CO detector we want to test. In this case, it's a Nest Protect smoke and CO detector in the box.

On the left, our CO Ambient sensor attachment for the Testo 300. On the right, our UUT, or “unit under test” — in this case, the Nest Protect Smoke and CO Alarm

Gianmarco Chumbe/CNET

The chamber houses two carbon monoxide detecting devices, a) the CO Ambient sensor portion of our control device, the TESTO 300, which is a combustion analyzer used by heating engineers who carry out installation and routine maintenance of industrial and residential heating systems, and b) the UUT (Unit Under Test), which takes the place of each carbon monoxide detector we tested for you. The chamber is sealed with foam but not air-tight, since we’re not particularly interested in making a CO bomb.

A close-up look at the gas regulator on the tank of CO used in CNET's carbon monoxide detector tests. There's a portable CO alarm attached to the line to help detect any dangerous leaks during our test process.

We use a portable CO alarm on the gas regulator to keep a nose out for leaks.

Gianmarco Chumbe/CNET

We installed a gas flow regulator on our tank to avoid pressure spikes, followed by a gas line to feed our gas mixture into the chamber. Two additional portable CO detectors are used. One near the valve, to ensure there are no leaks, and another that must be worn by the person carrying out the experiment to make sure there is no CO buildup in the test station area. On top of all that, our respirator suits and amply ventilated location ensure that we get a constant stream of fresh air at all times. This might all sound excessive, but it’s always good laboratory practice to put safety first, especially when you’re dealing with such a stealthy and prolific killer. 

We start by feeding our gas mixture to the chamber, closely monitoring the carbon monoxide concentration on the Testo. Once the concentration inside our chamber reaches at least 250 ppm or 400 ppm, we stop feeding the gas and start a timer. We want to assess how long the carbon monoxide detectors take to react to those conditions. As you may understand, we wanted to limit our exposure while making sure our results were repeatable.

Our results are summarized in the following table:

Carbon monoxide detectors: Response times

First Alert CO400 10:46 7:03First Alert Onelink 1042136 11:42 8:10First Alert CO615 12:12 8:07Kidde KN-COPP-B-LPM 14:10 8:40X-Sense SC07 20:05 7:50Nest Protect 06C 17:50 12:44Kidde KN-COB-DP2 20:22 10:53

  • Alarm response time at 250ppm
  • Alarm response time at 400ppm
Note: Time needed to sound alarm after exposure to different CO thresholds, mm:ss. Shorter bars indicate faster alarm times.

Other carbon monoxide detectors we’ve tested

Nest Protect Smoke and Carbon Monoxide Alarm : Very compelling option for those who don’t mind spending a little more in exchange for a wide range of smart features including location specific voice alarm, color-coded emergency notifications and smartphone app control for silencing and routine testing. Unfortunately, it underperformed its competition in our quickness of response test, with a bottom-three result in the 250ppm run and last place in the 400ppm run. Fortunately, it did a better job at quickly detecting smoke and fire hazards during our most recent round of smoke detector tests.

Kidde Battery Operated Carbon Monoxide Alarm – KN-COPP-B-LPM: Battery powered, digital display, test/reset and peak CO buttons, visual cues for alarm and operational status. Great unit if you want an affordable device that is capable of monitoring real-time CO levels as well as battery life. Not the fastest at detecting carbon monoxide (ranked 4th). CO readouts on its screen are the least accurate of the bunch, at 15% error, which is by no means the end of the world. 

X-Sense Combination Smoke and Carbon Monoxide Alarm: This combo unit comes equipped with a 10-year sealed lithium battery and a digital display that shows real-time CO concentration, battery level and working status. Second to last place in our quickness of response test, detecting CO at 250 ppm after 20 minutes. CO concentration monitor is accurate, less than 5% error. However, its LCD display is smaller than those of other products in this category, which makes it a little hard to interpret the readouts if you’re not close to the device. 

Kidde Plug-in Carbon Monoxide Alarm – KN-COB-DP2 Plug-in unit, backed up by two AA batteries. Features a single LED indicator and a test/reset button. Very specific brand and model requirements for battery replacements. The unit does not come with a cord extension so its installation placement is limited to an electrical outlet. Last place in our quickness of response test. 

Carbon monoxide detector FAQ

How do carbon monoxide detectors work?

Carbon monoxide detectors work by using sensors to detect the presence of CO in the air. When CO levels reach a certain threshold, the detector sounds an alarm to alert occupants of the building. There are different types of detectors available, but most use electrochemical sensors, metal oxide semiconductors, or biomimetic sensors to detect CO.

Where should carbon monoxide detectors be placed?

Carbon monoxide detectors should be placed on every level of the home and in every sleeping area. They should also be placed near sources of potential CO, such as furnaces, water heaters, fireplaces, and attached garages. Follow the manufacturer’s instructions for the specific placement of your detector.

How often should carbon monoxide detectors be replaced?

Carbon monoxide detectors should be replaced every 5-7 years, depending on the manufacturer’s recommendations. Regular testing and maintenance are also important to ensure that the detector is functioning properly and providing adequate protection.

What should I do if my carbon monoxide detector goes off?

Never ignore a carbon monoxide alarm. If your carbon monoxide detector goes off, evacuate the building immediately and seek fresh air. Call the fire department or emergency services from a safe location and do not re-enter the building until it has been checked and declared safe.

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