Updated March 2015
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On their own or as part of a network, CO detectors save lives

Carbon monoxide alarms come in many forms. Some are completely battery powered, while others plug into a standard AC outlet but have a battery backup to provide continuous protection even in the event of a power outage. Both types can be either stand alone or part of an interconnected network. If an interconnected CO detector is triggered, all alarms on the same network will sound, alerting those elsewhere in your home to possible danger. Stand-alone alarms won't trigger other alarms if they go off. For that reason, most experts recommend using interconnected alarms, and some states and cities require them in new construction. However, stand-alone alarms are cheaper, easier to install for homeowners, and can be an acceptable compromise if you want to primarily protect a single room or two, such as a bedroom.

Best CO and Smoke Detector

First Alert SCO501CN
First Alert SCO501CN

You can also get CO detection in a combination CO and smoke alarm. Those are covered in their own section, elsewhere in this report.

If you are most interested in a dedicated CO detector, the First Alert CO511B (Est. $40) looks like a terrific choice. It's feature packed, easy to set up and use and, while owner feedback is limited, expert feedback and the few comments we found from owners look strong.

This is an interconnected CO alarm that's part of First Alert's OneLink system. Rather than requiring an expensive and messy hard-wired installation, a radio interconnection is used to communicate between alarms. It's compatible with other First Alert OneLink alarms, including the First Alert SA501CN OneLink (Est. $45) photoelectric smoke detector profiled in our smoke detector report, and the First Alert SCO501CN (Est. $65), profiled in our section on combination CO and smoke detectors that's elsewhere in this report.

The feature list on the CO511B goes well beyond its radio link, but that's a good place to start. The OneLink 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 exceptionally well in expert testing. It draws a Recommended label in one independent review, 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 uniformly positive -- 4 stars or higher. Most say that installation is easy and that communication with other OneLink alarms -- smoke, CO or combination, and either battery operated or hard wired -- work 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 the best feedback for the Kidde KN-COP-IC (Est. $50). It's not been professionally tested, but we found more than 100 user reviews spread over sites such as Amazon.com and HomeDepot.com, and the majority are very pleased.

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; 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.

Stand-alone CO alarms are easy to install

While experts prefer interconnected CO detectors, stand-alone models provide basic but effective monitoring for single rooms or for situations such as rental homes or apartments, where an interconnected system can't be accommodated, or is simply overkill.

Among stand-alone CO alarms, we saw the best feedback for the First Alert CO615 (Est. $40). It draws a Best Buy rating in one expert test, and hundreds of mostly positive reviews from users at sites such as Amazon.com. The CO615 is AC powered, but no messy wiring job is required; instead, just plug it into a convenient outlet. While you can simply  plug this CO alarm into a low-mounted AC outlet,  First Alert also includes a six-foot extension cord in the package 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 CO2 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 let 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.

Expert testing looks good for the CO615, though it's judged to be a touch better at detecting higher levels of CO than lower levels in the most reputable professional test we spotted. 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 rates a 4.4-star rating at Amazon.com following more than 800 reviews.

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 First Alert CO400 (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. User reviews are generally positive, but the battery compartment draws some ire. Two versions of the CO400 are offered -- one with two AA batteries that mount from the front, or a model with a 9-volt battery (more common) that mounts from the rear. It's the latter that seems to present a nearly insurmountable challenge to some. That might be why First Alert has posted a video on this CO detector's product page that shows how it's done.

Elsewhere in this report:

Best Reviewed Carbon Monoxide Detectors: Hardwired or battery operated, interconnected or stand-alone, CO only or CO and smoke, these are the carbon monoxide alarms that experts and users say are the very best.

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 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.

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First Alert CO615 Dual Power Carbon Monoxide Plug-In Alarm with Battery Backup and Digital Display
Buy from Amazon.com
from Amazon.com
New: $59.99 $32.50   
In Stock.
Average Customer Review:  
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First Alert SCO501CN-3ST Interconnected Battery Operated Combination Smoke and Carbon Monoxide Alarm with Voice Location
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from Amazon.com
New: $139.99 $54.08   
In Stock.
Average Customer Review:  
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First Alert CO400 Battery Powered Carbon Monoxide Alarm
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from Amazon.com
New: $34.99 $11.11   
In Stock.
Average Customer Review:  
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First Alert SA501CN ONELINK Wireless Battery Operated Smoke Alarm
Buy from Amazon.com
from Amazon.com
New: $65.99 $42.95   
In Stock.
Average Customer Review:  
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First Alert CO511B Carbon Monoxide Detector, Wireless 9V Battery Powered OneLink w/ Voice Warning
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from Amazon.com
New: $35.87
In Stock.
Average Customer Review:  
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Kidde KN-COP-IC Hardwire Carbon Monoxide Alarm with Battery Backup and Digital Display, Interconnectable
Buy from Amazon.com
from Amazon.com
New: $61.99 $40.89   
In Stock.
Average Customer Review:  

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