Experts say you should look for the following when choosing a carbon monoxide detector. Only products that meet the Underwriters Laboratory (UL) 2034 Standard (1998 revision) are acceptable. Check the package for the UL symbol with the adjacent phrase "single station carbon monoxide alarm," and check the back of the model for the manufacturing date, which should be after Jan. 1, 2000. Other certifying agencies are the International Approval Services (IAS-696) and Canadian Standards Association (CSA 6.19-01). These three agencies have similar requirements.

In 1998, Underwriters Laboratory (UL) revised its standards for carbon monoxide detectors. However, manufacturers didn't implement the new specifications until Jan. 1, 2000. Now, all UL-listed units will not indicate carbon monoxide levels below 30 parts per million (ppm), and must not trigger the alarm for levels below 100 ppm. However, the alarm must sound if carbon monoxide levels remain at 70 ppm for one hour. (The maximum allowable concentration set by OSHA, the Occupational Safety and Health Administration, is 35 ppm, but first symptoms of headache, fatigue, dizziness and nausea don't start until exposure to 200 ppm for two to three hours.) All UL-listed carbon monoxide alarms must also have a manual silence button, but if elevated CO levels continue, the alarm must resound every six minutes.

  • The carbon monoxide detector should have an 85-decibel alarm. This is loud enough to wake you and your family. Experts recommend having a detector for each floor of your home.
  • Experts recommend carbon monoxide alarms with a digital display. These continually show carbon monoxide gas levels, as well as a peak-level memory feature.
  • Look for models with a test button, which allows you to check that the alarm is functioning properly. As mentioned above, this checks the electric circuitry but not the gas sensor, which requires an additional test. This button should turn the unit off or reset it after an alarm is triggered, while allowing the alarm to sound again within six minutes if carbon monoxide is still present.

In addition, these are some additional usage guidelines:

  • Install at least one CO detector on every floor of your home and outside sleeping areas.
  • Install detectors according to manufacturer's instructions. Do not place detectors within five feet of household chemicals. If your detector is hardwired directly into your home's electrical system, you should test the unit monthly. For battery-operated units, test the detector weekly and replace the battery at least once a year.
  • Avoid placing your detector directly on top of or directly across from fuel-burning appliances because these appliances emit some CO when initially turned on.
  • If your alarm sounds, immediately open windows and doors to ventilate. If the problem is not obviously fixable, evacuate the house and call the fire department. Follow-up with a checkup by a professional.
  • Replace detectors every five years unless the manufacturer specifies a shorter or longer life.
  • Do not connect plug-in units to an electrical outlet that is controlled by a light switch.
  • Select a detector that is battery-operated or with battery backup to ensure monitoring during a power outage. In addition, a backlit digital display allows users to view CO levels in the dark.

Placement of a carbon monoxide detector is also important. Because CO gas is lighter than oxygen, it tends to float higher up in a room. That means the optimal placement for a CO detector is high up on the wall -- and not many people have electrical outlets that high up. A battery-operated model is the best choice if you want the most placement flexibility. But if you're concerned about changing the batteries regularly, a plug-in CO detector that's placed lower on a wall is certainly better than no detector at all.

If you only want to install one carbon monoxide detector, experts say it should be placed near the bedrooms so its alarm can wake you while sleeping. For multilevel homes, consider installing a detector on each level. Heating and cooking appliances are usually the main producers of CO gas, but you don't want to install your carbon monoxide detector right next to these appliances because you could end up with false alarms (because they can emit a small amount of CO gas on startup). A carbon monoxide detector should not be placed within about 15 feet of a stove or furnace, or in very humid areas such as bathrooms.

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