Guard Against Carbon Monoxide

When buying a detector, you can choose among those that are battery-powered, those that plug into electrical outlets or are hard-wired into your electrical system. Hard-wired detectors are more expensive, but also more reliable and longer-lasting. They are recommended by fire departments, security services and personal injury lawyers who deal with these cases.

Consider whether you want your carbon monoxide detector to work in concert with your smoke alarm. That is, when there's a threat from smoke or carbon monoxide, the same alarm sounds. Some security services monitor these threats as well as others, so check with your service.

Alarms can be stand-alone or interconnecting. Interconnecting alarms communicate with each other so that if one alarm in the house is tripped, they all sound. They're recommended for multistory houses.

Other considerations in purchasing a detector are what levels of gas trigger the alarm, whether the alarm is voice, digital or beeping, and the type of sensory mechanism. Some alarms speed up or get louder as the threat continues.

The goal of all detectors is to provide the greatest margin of safety before the carbon monoxide affects your sense of time and judgment -- and thus how quickly you can get fresh air before you are incapacitated.

Detectors use various types of sensors to measure gas levels. Burger's favorite kind uses a metallic oxide, also known as tin oxide or stannic oxide. "They are mechanically simple and are electronic in nature; therefore, they are very long-lived and very reliable," he said. Experience shows they should last for more than 10 years, he said.

No type of detector lasts forever, he said. Eventually, all will give false readings, so they should be replaced as they're expected to wear down. While some types may last 10 years, others may last only two or three. Follow the manufacturer's recommendations for replacement.

In the September issue of its magazine, Consumer Reports rated carbon monoxide detectors using these criteria and others. Detectors with warnings that become louder or faster at increasing levels and digital displays are preferred. (The ratings are also on the magazine's Web site, http://www.consumerreports.org/ , which requires a paid subscription.)

For multifloor houses, Consumer Reports prefers an interconnecting system. Most of these are hard-wired, but the product ratings group gave its top nod in this category to what it terms a "winning wireless," a system that allows alarms to communicate with each other wirelessly. This alarm, First Alert's OneLink smoke and carbon monoxide alarm, is a battery-powered detector. Its alarm, a recorded voice, tells you where the problem is, whether it's carbon monoxide or smoke, and if it's carbon monoxide, how much there is. This alarm costs $75.

The group's second-rated interconnecting alarm, Kidde's Nighthawk smoke and carbon monoxide combo, is hardwired to the electrical system, with a battery backup. It costs $50.

Consumer Reports rated stand-alone alarms separately. The top pick in that category is an American Sensors unit at $65 (model CO920), with a Kidde unit for $40 as the best value for the price (model KN-COPP-B).

Among other tips from Consumer Reports: Check with the building inspector in your municipality to see what legal or mechanical requirements apply to you, if any. Always buy the latest version of a detector because so it will be the most up-to-date and most sensitive.

"All of these [carbon monoxide] alarms sounded within 10 minutes for high levels of carbon monoxide and 30 minutes for lower levels," the group said in its report. "Models that scored higher responded fastest, providing an extra margin of safety at higher levels, where [carbon monoxide] can affect your sense of time and judgment."

Don't place a detector right next to a fireplace or flame-producing appliance, and keep it out of the reach of pets and children. Also, make sure it won't be covered by drapes or furniture.

Do put detectors near sleeping areas. Make sure the alarms are loud enough to wake you and other household members. Install the detectors about five feet above the floor, or on the ceiling, because carbon monoxide is slightly lighter than air and therefore rises.