First Alert CO511B
First Alert CO511B

Best 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 OneLink alarms. 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.
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First Alert CO615
First Alert CO615

Best stand-alone carbon monoxide detector

The First Alert CO615 is an effective and easy-to-use plug-in carbon monoxide detector. It can't be interconnected with other CO alarms, but provides an ideal solution if you just want a carbon monoxide detector for a single room, or a small apartment where an interconnected system doesn't make sense. Even though it doesn't display CO levels continuously, the large LCD readout is a plus.
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First Alert CO400
First Alert CO400

Cheap carbon monoxide detector

The First Alert CO400 is a basic carbon monoxide detector that runs on batteries, giving users more placement options than plug-in models. At five years, the lifespan is lower than some CO detectors, but that's not a troubling trade-off considering the price. There are no fancy features, nor is the alarm interconnectable, but the CO400 is a suitable choice for those who just want a competent CO monitor at the lowest possible cost.

First Alert SCO501CN
First Alert SCO501CN

Best CO and Smoke Detector

If you need both smoke and CO alarms, the First Alert SCO501CN is a practical and cost-effective choice. It provides protection from smoky fires as well as dangerous CO. It's completely battery powered and will wirelessly interconnect with other OneLink smoke, CO or combination alarms to alert you to danger in any part of your home. It features a voice alert in addition to a standard horn that will announce the location of the hazard on all compatible alarms in the system.
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Stand-alone carbon monoxide and smoke detector

The Kidde KN-COSM-BA is a stand-alone combination detector, guarding against both smoke and carbon monoxide. Unlike the First Alert SCO501CN, there's no interconnectivity. It does have a voice alert, however, that will identify the hazard type (smoke or CO). It also uses an ionization rather than a photoelectric smoke sensor -- meaning that it's more effective than the SCO501CN when it comes to detecting raging fires, but less so when the hazard is a smoldering one. The KN-COSM-BA is completely battery operated, so installation is easy.

Nest Protect
Nest Protect

Smart carbon monoxide and smoke detector

The Nest Protect is the first of what could be a wave of "smart" carbon monoxide and smoke detectors. It's an interconnected system that also interfaces with the Internet. That allows for updates to fix bugs -- such as one that minimized false alarms caused by steam -- and add future features. It also allows you to keep tabs on your home even when you are away via a smartphone or tablet app. The feature that allowed alarms to be silenced with the wave of the hand has been removed following a recall, and a corresponding price cut. Expert reviews are highly positive, but user reviews are more mixed, indicating that the Next Protect is probably best for those willing to endure the ups and downs that go with riding on the leading edge of technology.

See a side-by-side comparison of key features, product specs, and prices.

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, and 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. We delve more deeply into the specific Dangers of CO gas elsewhere in this report.

Every home should have a CO detector, even if you don't have any gas, oil or wood-fired heating systems or appliances. A car accidentally left running in an attached garage, a neighbor with a malfunctioning appliance in an attached dwelling, or the accidental misuse of a standalone heating device during a power outage can all expose you and your family to CO gas.

When shopping for a CO detector, you will find that there are several different options to choose from:

Stand-alone carbon monoxide detectors work independently. These 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 won't trigger other alarms in the home if they detect CO.

Interconnected carbon monoxide detectors form a network of alarms within your home. 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. These can be made part of a network that also includes smoke detectors (which are reviewed in their own report). 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. The disadvantage is that they can be the hardest to install. That's especially true of those that rely on a wired connection as a circuit has to be run to all the alarms in the system -- a task that's much easier to do during construction or a major renovation than as an add-on to an existing structure. However, wireless interconnected CO detectors can be installed by virtually anyone and don't require any rewiring. Each detector can relay signals from one to another, setting up a mesh network that can cover your entire home.

Combination CO and smoke detectors are also available. These provide protection against both types of hazard in one unit. They are generally pricier than stand-alone models, but can be cheaper than buying separate units for CO and smoke. Combination units  can be stand alone or interconnected, hardwired or battery operated. This category also includes the latest smart smoke detectors, such as the Nest Protect (Est. $100), which is an interconnected smoke and CO detector that can also send an alert to a smartphone or tablet to warn you about a situation while you are away from home. The Nest smoke and CO detector was the subject of a recall in 2014 -- a feature that allowed users to silence an alarm with the wave of a hand also sometimes caused an alarm to fail to sound if there was nearby activity -- but that's since been addressed with a software update.

Finding the best carbon monoxide detectors

The best CO detectors operate reliably in the case of an emergency, without driving you to distraction with false alarms. They should also be easy to install, easy to test, and easy to silence if the need arises. To find the best carbon monoxide detectors, we looked at expert tests, such as those conducted by, and melded that with feedback from happy as well as harried homeowners to determine which detectors worked well over the short and long haul, and which ones disappointed. User reviews were drawn from a number of sites, including, and more. We then rated CO detectors on their performance, ease of use and durability to find the best choices.

Elsewhere in this report:

The Dangers of CO: What is carbon monoxide, and why do you need to be worried about it?. Our editors lay out the facts and explain how to effectively protect yourself and your loved ones from this silent, deadly threat.

Best Carbon Monoxide Detectors: Whether you want a simple alarm for your bedroom, or to put together a system that can alert you to danger in any room, these are the top CO-only alarms.

Best CO and Smoke Detectors: If you need a detector for both smoke and carbon monoxide, these all-in-one alarms can reduce clutter and save money. Smart combination detectors that connect to the Internet are discussed, too.

Buying Guide: Not sure which CO or combination detector is best for your home and your budget? Our editors explain the considerations and point out what to look for to make the right choice.

Our Sources: Where can you learn more about CO detectors? These are the expert and user reviews we consulted to find the top stand-alone and combination CO detectors.

Nest Protect Smoke Plus Carbon Monoxide, Battery S2001BW
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