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Plug-in CO detectors are easy to use, but lack advanced features

For most owners, the easiest carbon monoxide detectors to install and operate are plug-in models. Praised for its reliability and simplicity, the First Alert CO615 (Est. $30) garners the most positive feedback from professional testers and individual owners. This plug-in model will run on battery backup for a short time in the event of a power outage, but it won't eat through batteries like some competing models. It is also equipped with a digital display for those who want to view current carbon monoxide levels at the press of a button.

The most common complaint about the CO615 is its flimsy battery compartment door. The door doesn't always close properly after batteries are installed, but this flaw doesn't appear to interfere with the unit's operability. Many users solve the problem by simply taping the door shut. Although it is a plug-in, the unit will not run without its batteries installed, and there is no option to bypass this feature. In addition, if the battery compartment door is forced closed, it may break.

Still, most reviews are highly positive. This carbon monoxide detector earns recommendations from a professional testing organization and good feedback from owners as a result of its reliability and ease of installation and use.

While other First Alert plug-in models cost a bit less, they also have fewer convenience features. Our plug-in runner up, the Kidde KN-COPP-3, costs about $15 more. But some owners prefer the Kidde unit because it continuously displays CO levels and allows them to monitor peak CO levels. However, it uses a 9-volt battery, and some users complain it won't run for long in battery-backup mode.

Battery-operated CO detectors are simple yet effective

Homeowners who want the flexibility to place carbon monoxide detectors in different locations favor battery-operated units. The First Alert CO-400 (Est. $20) is a battery-operated unit that is reliable and easy to use, but does not come with lots of bells and whistles.

Small and inconspicuous, the CO-400 can be wall-mounted or placed on a shelf; owners appreciate that they don't have to sacrifice an outlet for this unit. This First Alert unit will sound its 85-decibel horn if it detects carbon monoxide, but it does not have a display and doesn't issue verbal warnings.

It's hard to find many competing models in the First Alert CO-400's price range. For example, the Kidde KN-COPP-B-LP is at least $10 more, but it has considerably more features. It displays current CO levels and has a peak-level memory function. However, some owners complain of getting random peak level readings even after they reset their units. Other models with similar features receive positive feedback from owners, but the First Alert CO-400 receives the most consistent praise for its intuitive design.

The CO-400 does receive a handful of negative reviews for the battery compartment door, which some owners say is flimsy and easy to break. Moreover, the unit will not operate without properly installed batteries, and several owners say they broke the door trying to force it closed. Aside from the battery door, this model doesn't have many mechanical problems. Owners appear to be happy with the First Alert CO-400; it's reliable, easy to use and its sensors last five years.

Combination alarms provide convenience

Owners appreciate combination alarms because they can detect both smoke and carbon monoxide. Our top-rated unit, the Kidde KN-COSM-B (Est. $35) , has ionization smoke sensors, which detect fast flaming fires. Because of this, owners say the alarm seems sensitive to cooking smoke and should be placed away from the kitchen. However, one of the best features of this unit is its verbal warnings -- "Fire! Fire!" and "Warning! Carbon monoxide!" – as well as a low-battery alert and Hush Mode for silencing the alarm.

Another top combination unit, the Kidde KN-COSM-1B , is the hardwired version of the Kidde KN-COSM-B. It also gives verbal warnings and interconnects with other Kidde units. However, some users complain that it tends to give false alarms during power fluctuations and doesn't run on its 9-volt battery backup for long. Neither of these Kidde models has a display.

Still, the Kidde KN-COSM-B has a loyal following and mostly positive owner reviews. Owners say it is effective, its sensors last seven years and its three AA batteries are easy to change. It is a sturdy, but compact, model that can be moved around as needed.

Other combination alarms to consider include options with both ionization technology (to detect flames) and a photoelectric smoke sensor (to detect smoldering fires). However, photoelectric alarms tend to cost more, and this is reflected in the higher price.

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First Alert CO615 Dual Power Carbon Monoxide Plug-In Alarm with Battery Backup and Digital Display
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Kidde KN-COSM-BA Battery-Operated Combination Carbon Monoxide and Smoke Alarm with Talking Alarm
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First Alert CO400 Battery Powered Carbon Monoxide Alarm
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New: $34.99 $16.79   
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