Home > Home & Garden > Carbon Monoxide Detectors > Carbon Monoxide Detectors

Best Carbon Monoxide Detectors

By: Carl Laron on March 14, 2018

Editor's Note:
Whether you want a cheap stand-alone alarm, or an advanced interconnected one, these First Alert and Kidde CO alarms can are top-rated according to experts and users. They all meet UL standards, and do a great job of detecting carbon monoxide, which is odorless, colorless and deadly. That's why CO detectors are a must have in any home.

First Alert CO615 Review
Best Reviewed
Specs that Matter Power source -- AC with battery back up Interconnected -- No Dimensions (W x D x H) --4.8" x 1.7" x 3.3"

Best carbon monoxide detector

The First Alert CO615 is an effective and easy-to-use carbon monoxide detector. AC powered with a battery backup, it can plug directly into any outlet, though a better choice is using the included 6-foot power cord to mount it high on a wall per expert recommendations. It's excellent at detecting high and low CO levels and the large LCD readout is a plus.

Buy for $25.59
KN-COB-LP2 Review
Best Reviewed
Specs that Matter Power source -- Battery Interconnected -- No Dimensions (W x D x H) -- 4.5" x 1.5" x 2.75"

Best cheap carbon monoxide detector

The KN-COB-LP2 is a basic, battery-operated carbon monoxide detector that's easy to install and use. There are no fancy features, just a test/reset button and a pair of LEDs to indicate that the unit is operating correctly or if an alarm has sounded. It meets UL standards regarding sensitivity, with a loud alarm that's rated at 85 dB at a distance of 10 feet.

Buy for $19.84
First Alert CO511B Review
Best Reviewed
Specs that Matter Power source -- Battery Interconnected -- Yes Dimensions (W x D x H) -- 5.3" x 2.38" x 5.3"

Best interconnected carbon monoxide detector

For maximum protection, experts recommend interconnected CO detectors such as the First Alert CO511B. This CO alarm is completely battery powered and uses secure radio links to communicate with other First Alert wireless alarms, including smoke and combination models. It's judged to be excellent in detecting dangerous carbon monoxide levels. When triggered, voice alarms announcing the hazard and the specific location will sound on all connected alarms, minimizing confusion.

Buy for $39.13

Types Of CO Detectors

Stand-Alone Carbon Monoxide Detectors

These carbon monoxide detectors work independently. They can be battery operated or plug into an AC socket (with a battery backup in the event of a power failure). They are the easiest type to install, but don't have the ability to trigger other alarms in the home if they detect CO.

Interconnected Carbon Monoxide Detectors

This type of CO detector connects to other alarms in your home to create a network. The connection can be hard wired or wireless, and the alarms can either plug into an AC outlet (with battery backup) or be completely battery operated. The advantage of an interconnected network is that when any one alarm sounds, they all sound, giving you an early warning of danger in a remote room, or one that's otherwise currently unoccupied.

You can also find CO detectors that are part of a combination alarm that includes a smoke detector. There are pluses and minuses to these types of alarms, but if you think one is right for your situation, combination smoke and CO detectors are covered in detail in our smoke detector report.

Carbon monoxide detectors save lives

Carbon monoxide (CO) is a potentially deadly, odorless and colorless gas that is estimated to kill approximately 500 people a year and sicken many others. Often called the "silent killer," CO is a by-product of incomplete combustion and comes from malfunctioning appliances, such as gas or oil furnaces, wood burning stoves, or gas clothes dryers. When these appliances are not adequately ventilated, or if they malfunction, carbon monoxide can build up in the home to lethal levels. The list of potential sources of carbon monoxide also includes a wealth of items that shouldn't be used indoors under any circumstances, including propane heaters, portable generators and charcoal grills. Unfortunately, people don't always follow safety instructions and may use these items improperly.

According to MedlinePlus, a service of the National Institutes of Health, CO is the leading cause of poisoning in the United States. As noted by the Centers for Disease Control and Prevention (CDC), everyone is at risk from CO poisoning, though infants, the elderly and those with certain conditions, such as heart disease, are most at risk. If you are exposed to CO gas, you may notice symptoms such as headache, dizziness, weakness, upset stomach, vomiting, chest pain, and confusion, the CDC notes. If you are asleep, especially if you're intoxicated, your chances of dying from CO exposure are greatly increased. If you survive, recovery can be slow, and there is a chance that permanent brain damage can occur.

The good news is that CO poisoning is highly preventable and the CDC's site has a long list of mostly common-sense steps to take. Those include servicing gas, oil or coal-burning appliances regularly, and not using items such as charcoal grills and camp stoves that are intended for outdoor use indoors. At the top of the list, however, is this advice:

"Install a battery-operated or battery back-up CO detector in your home and check or replace the battery when you change the time on your clocks each spring and fall."

All carbon monoxide detectors have a finite lifespan with sensors that wear out within five to seven years. However, the newest detectors come equipped with an end-of-life timer. When the time is up, the devices essentially self-destruct -- beeping at a regular interval until replaced. Don't just trust the timer, though. The National Fire Protection Association (NFPA) recommends that you "Test CO alarms at least once a month; replace them according to the manufacturer's instructions."

Make sure your CO detector is UL certified

All of the CO alarms in this report meet Underwriters Laboratory standards (UL2034) designed to alert people well before CO exposure becomes life threatening, but also to prevent nuisance alarms (caused by things such as typical air pollution or normal short-term emissions from properly operating appliances) that can cause homeowners to tune out CO alarms, greatly reducing a detector's effectiveness. They don't respond at all to very low CO levels below 30 parts per million. Once CO levels reach 30 ppm, they won't sound until after 8 hours of continuous exposure. At 70 ppm, they won't sound for at least 60 minutes, but must sound after 4 hours. At 150 ppm, there's a 10 minute delay, but the alarm will sound before 50 minutes have passed. Finally, at 400 ppm, there's a brief 4 minute delay, and the alarm must sound before 15 minutes.

However, not every CO detector available at retail meets UL standards. Last year, Consumer Reports rated three models it bought from online retailers, including Amazon and Ebay, as "Don't Buy." Those models were the NetBoat WB_H3110061, Foho YJ-806 and GoChange 882. They lacked any evidence of UL certification, and when tested by Consumer Reports, performed inadequately -- either failing to sound at lower concentrations of CO, or responding too quickly at any level, making it more likely that consumers would ignore warnings as nuisance alarms. The retailers removed those models, and similar ones, from their websites once informed of the issue, Consumer Reports said, though also adding that they may still be available on other sites. Consumer Reports also recommends that you check your existing alarms and if they lack either the UL symbol or a statement that they been otherwise tested by another lab and meet UL2034 standards, they be replaced.

The bottom line, then, is that if a CO alarm sounds, the situation merits concern and you should respond immediately. The NFPA says to do the following: "Move to a fresh air location outdoors or by an open window or door. Make sure everyone inside the home is accounted for. Call for help from a fresh air location and stay there until emergency personnel [arrive]."

The best carbon monoxide detectors

Among stand-alone CO alarms, we saw the best feedback for the First Alert CO615 (Est. $35). It's the only stand-alone CO alarm to earn a Recommended rating from Consumer Reports. It also draws nearly 1,600 mostly positive reviews from users posting at Amazon. The CO615 is AC powered, but no messy wiring job is required; instead, just plug it into a convenient outlet. While you can simply use a low-mounted AC outlet, the AC adapter is removable and is equipped with six-foot extension cord for placement "flexibility." This allows those looking for the best protection to place the detector higher on the wall (at least five feet above the floor) per the recommendations of most experts. Two AA batteries provide backup for continuous monitoring, even when AC power is out.

The CO615 isn't the most feature packed CO detector, but there are a few nice touches. The LCD display won't display continuous CO levels, but can show the peak CO levels over the last 24 hours at the touch of a button. The warning chirp if the back-up batteries become low can be silenced for eight hours. Some sites continue to list the existence of a feature that lets you silence the battery back-up warning with any standard IR remote control, but that feature proved to be problematic and has since been dropped.

Testing looks good for the CO615. It earns the top rating at Consumer Reports for its ability to detect high and low levels of CO. Like all CO alarms in this report, it meets UL2034 standards for its ability to issue warnings that protect life without subjecting users to nuisance alarms.

User reviews are also highly positive. We noted some gripes about build quality, particularly a battery door that's sometimes called flimsy, and a few found the CO detector challenging to use, or claimed that it arrived defective. However, those are well offset by a majority that seem mostly-to-completely pleased with the CO alarm. It earns a 4.5-star rating at Amazon.

If you prefer Kidde products, the Kidde KN-COPP-3 Nighthawk (Est. $30) is similarly priced, and similarly well-liked by users. However, in expert testing, the CO615 is judged to be a step better at detecting low levels of CO (though the Nighthawk is still very good in that regard), and is said to have a higher-quality/more-effective display. Still, users at Amazon rate the Kiddie an identical 4.5 stars, and that's based on even more reviews -- over 2,550.

Like the First Alert, the KN-COPP-3 is designed to be plugged into an existing outlet, but, again, is equipped with a removable adapter for mounting higher on a wall or on a tabletop. Most users are extremely pleased, though we did see some comments claiming that the unit burns through back up batteries even when plugged in.

For those looking for a competent, easy-to-install carbon monoxide detector at the lowest possible price, things don't get much more basic than the KN-COB-LP2 (Est. $17). This CO alarm is battery powered, which gives you all the installation flexibility you might need -- though again it might be wise to heed expert advice to install it high above the floor. There's little in the way of features -- no readouts or voice warnings here -- just a button to silence nuisance alarms and a pair of LEDs to indicate that the unit is operating or if an alarm is sounding.

User reviews are generally positive, though complaints about defective units or excessive battery usage are not unheard of. Still, Amazon users rate the carbon monoxide alarm a solid 4.6 stars based on more than 450 reviews. At Home Depot, where this model is sold under the Code One brand, it earns an equally impressive score of 4.5 stars after more than 500 reviews, with recommendations from 95 percent of users.

Interconnected alarms can provide an early warning

While users tend to prefer the simplicity of stand-alone alarms, experts often prefer interconnected ones that can alert homeowners to issues in areas that are currently unoccupied. Among interconnected choices, we see good expert feedback for the First Alert CO511B (Est. $45). It's feature packed and easy to set up and use.

Many interconnected CO alarms require a messy and expensive hard-wired installation, but the CO511B (sometimes also sold as the First Alert CO511) uses a radio signal is used to communicate between alarms. It's compatible with other First Alert wireless alarms, including some models of smoke alarms and combination CO and smoke alarms; see our report on smoke detectors for more information.

The feature list on the CO511B goes well beyond its radio link, but that's a good place to start. The system establishes a mesh network, independent of other networks, such as Wi-Fi within your home. Each alarm acts both as a receiver and a transmitter, allowing the network to extend further. Security codes and frequency hopping technology establish stable and secure communications between alarms.

Other features include a voice alert that includes location information so that you won't be left guessing which alarm has sounded; up to 11 locations, such as a basement, can be programmed. Latching technology provides a visual indication of which alarm sounded after the alert has shut off. It also gives you a visual indication of which unit has a low-battery condition. The alarm tone sweeps through low frequencies to aid those with age-related or other hearing loss.

The First Alert CO511B does well in expert testing by Consumer Reports, with top ratings across the board for detecting high and low CO levels and for the quality of its voice alerts. User reviews, while not plentiful, are generally positive. Most say that installation is easy and that communication with other interconnectable First Alert alarms -- smoke, CO or combination, and either battery operated or hard wired -- works as advertised.

While the First Alert CO511B is a great choice for homeowners looking to add CO protection with a minimum of muss and fuss, if you are adding carbon monoxide alarms as part of new construction or a major remodeling job, you, or your contractor, might prefer a hardwired unit. The First Alert CO511B is completely battery powered and, while battery life should be reasonable, the batteries will need to be replaced periodically.

A hard-wired CO alarm should have a battery as well (though not all do) to provide constant monitoring even during power outages; however, it's only a back-up, the main power will draw from your home's AC wiring. Among hardwired interconnected CO detectors, we saw good feedback for the Kidde KN-COP-IC (Est. $45). It's not been professionally tested, but we found over 160 user reviews at Amazon, and the majority of owners are pleased as it earns a 4.6 star rating. Reviews at other sites are less plentiful, but equally positive; a 4.7 star rating at Home Depot based on over 30 reviews, for example.

Like the First Alert CO511B, the Kidde KN-COP-IC can be used in a network of compatible Kidde alarms, including smoke and combination CO and smoke detectors, interconnected via a simple wired network. Installation is reported as easy as long as walls are down (as part of a larger remodeling project, for example) or a compatible Kidde alarm network is already in place; otherwise you might want to enlist the aid of an electrician to run the connections between units.

Installation considerations aside, The KN-COP-IC looks to be a fine unit. It lacks some of the features found in the CO511B, such as a voice alert, but adds others that the First Alert alarm lacks. Chief among those is a readout that displays CO levels, updated every 15 seconds. It also has a peak memory that can recall the highest CO level measured since the alarm was last reset.

Expert & User Review Sources

While there are a number of sites that report on CO detectors, the only one we spotted that does current, credible testing is Consumer Reports. Editors there rate each detector on its ability to respond to both high and low levels of CO, and the quality and accuracy of the display or, if a feature of the tested alarm, voice message. Beyond that, we looked to the feedback from owners posting at sites such as Amazon, Home Depot, Lowe's and elsewhere. That feedback is extremely helpful in assessing things such as ease of installation and reliability -- including freedom from excessive false alarms.

Recently Updated
Carbon Monoxide Detectors buying guide

What every best Carbon Monoxide Detectors has:

  • UL Certification.
  • A loud alarm.
  • Testing functionality.

Read More »

Learn More »