Carbon Monoxide Detectors - How a CO Alarm Works - What To Do If Alarm Sounds

If CO does find its way into your home, the levels may build, creating a dangerous situation. In the UL2034 Standard, Underwriters Laboratories specifies response times for CO alarms as follows:

  • At 70 parts per million: Unit must sound alarm within 60-240 minutes.
  • At 150 parts per million: Unit must sound alarm within 10-50 minutes.
  • At 400 parts per million: Unit must sound alarm within 4-15 minutes.


Carbon monoxide is a by-product of combustion, present whenever fuel is burned. It is produced by common household appliances such as gas or oil furnaces, clothes dryers, water heaters, ovens and ranges. A charcoal grill operating in an enclosed area, a fire burning in a fireplace or a car running in an attached garage also produce carbon monoxide.

According to the Journal of the American Medical Association (JAMA), carbon monoxide is the number one cause of poisoning deaths in the U.S.A. Making sure furnaces and other potential carbon monoxide sources are properly vented and in good working condition, along with owning a UL listed carbon monoxide detector, could become a matter of life and death.

But what do you do and who to you call when your carbon monoxide detector goes into alarm?

If the alarm goes off, immediately move to a location that has fresh air. Do a head count to be sure all persons are accounted for. Call the fire department. Do not re-enter the premises until it has been aired out and the problem corrected.

To identify the source/s of carbon monoxide, have a professional check the following :

  • Gas or oil furnaces are frequently the source of carbon monoxide leaks. Measure concentrations of carbon monoxide in flue gases. Check all connections to flue pipes and venting systems for cracks, gaps, rust, corrosion or debris. Check the filters and filtering systems for dirt and blockages. Check the combustion chamber and heat exchanger for cracks, holes, metal fatigue or corrosion.
  • Check furnace flame, burners and ignition systems. A predominately yellow, flat, lazy-looking flame in a natural gas furnace indicates fuel is not burning efficiently and is thus releasing higher than usual levels of carbon monoxide. Oil furnaces with a similar problem produce an 'oil' odor, but remember you can't smell, see or taste carbon monoxide.
  • Chimneys and venting systems must be carefully checked for blockages caused by debris, animal nests, cracks, holes or cave-ins. A blocked chimney or venting system can force dangerous gases back into your home.
  • Venting and fan systems on all fuel burning appliances must be inspected for proper installation to assure carbon monoxide is vented out rather than in. Don't forget gas water heaters, clothes dryers, space heaters or wood burning stoves.
  • Inspect fireplaces for blocked or bent chimneys or flues, soot and debris or holes in the chimney that could release carbon monoxide exhaust back into the home.
  • Stove pilot lights in a closed-up home can be a source of carbon monoxide build-up if not operating properly because they are not vented to the outside. Check to be sure they are operating properly.
  • Fireplace pilot lights can also produce carbon monoxide and should be checked regularly.
  • Never burn charcoal inside no matter how much you want to recapture summer and never use your gas stove as a heater. Keep the oven door closed and use it for cooking only.
  • Never leave a car running in an attached garage even if the garage door is open.

Taking time to understand the characteristics of carbon monoxide and how Underwriters Laboratories, Inc. (UL) listed carbon monoxide detectors work could save your life.

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Carbon Monoxide Detectors w/ PPM Displays and Battery Backup

Although all home carbon monoxide detectors use an audible alarm signal as the primary indicator, some versions also offer a digital readout of the CO concentration, in parts per million.

Typically, they can display both the current reading and a peak reading from memory of the highest level measured over a period of time.

The digital models offer the advantage of being able to observe levels that are below the alarm threshold, learn about levels that may have occurred during an absence, and assess the degree of hazard if the alarm sounds.

They may also aid emergency responders in evaluating the level of past or ongoing exposure or danger.