Detecting a silent killer: carbon monoxide

It would be ideal if we could deal at the source with carbon monoxide — that odorless, colorless yet potentially deadly gas that results from burning wood, natural gas, oil and kerosene. The best way is to have furnaces and fireplaces serviced regularly.

But things can happen, even when you're being diligent. So every house should have at least one carbon-monoxide detector/alarm.

Need to know: Detectors trigger an alarm based on an accumulation of carbon monoxide over time. Carbon monoxide can harm you if you are exposed to high levels of it in a short time or to lower levels over a long period. The alarm warns you of the danger before you begin to experience symptoms such as headache, dizziness, nausea, weakness, vomiting and shortness of breath.

If anyone in the house shows symptoms, leave immediately and call 911; air out the premises; and call a professional to check appliances, chimneys and furnaces.

Be sure to: Buy a detector with a backup battery. Many situations in which carbon monoxide plays a role occur during power outages.

Operating manual: Carbon monoxide is slightly lighter than air; it also may be contained in warm air rising from appliances. So conventional wisdom suggests placing the detector on a wall about 5 feet above the floor, or on the ceiling. It's a good idea to have a carbon-monoxide detector on every floor.

Never put one close to a fireplace or a gas stove or oven that produces a flame. Keep the detector 15 feet from furnaces or water heaters; close proximity likely will set off the alarm.

Don't do this: 500 people die each year from non-fire-related carbon-monoxide poisoning. To keep carbon monoxide from building up in your home, don't use a generator, charcoal grill, camp stove or other gasoline- or charcoal-burning device inside the house, the basement, the garage or near a window. Don't run a car or truck inside a garage attached to your house, even if you leave the door open. Don't burn anything in an unvented stove or fireplace, and don't use a gas oven to heat the house.

What it will cost: A detector that meets standards established by Underwriters Laboratory costs from $40 to $80. UL Standard 2034 requires that home carbon-monoxide detectors must sound a warning before carbon-monoxide levels reach 100 parts per million over 90 minutes, 200 parts per million over 35 minutes or 400 parts per million over 15 minutes.

A carbon-monoxide detector does not replace a smoke alarm. However, there are combination smoke alarm/carbon-monoxide detectors. First Alert's model (about $40) uses a different-sounding alarm for each danger. The Kidde Nighthawk combo detector (about $50) even has a voice alarm that announces if it has detected smoke or carbon monoxide, or if the batteries need replacing.