Frequently Asked Questions About Carbon Monoxide Detectors


The Consumer Products Safety Commission (CPSC) reports that approximately 200 people per year are killed by accidental carbon monoxide (CO) poisoning with an additional 5000 people injured. These deaths and injuries are typically caused by improperly used or malfunctioning equipment aggravated by improvements in building construction which limit the amount of fresh air flowing in to homes and other structures.

While regular maintenance and inspection of gas and oil burning equipment in the home can minimize the potential for exposure to CO gas, the possibility for some type of sudden failure resulting in a potentially life threatening build up of CO gas always exists.


What are the different types of carbon monoxide detectors and how do they work?

There are a number of different types and brands of carbon monoxide detectors on the market today; They can be most easily characterized by whether they operate on household current or batteries. Underlying this, in most cases, is the type of sensor employed in the detectors operation. Detectors using household current typically employ some type of solid-state sensor which purges itself and resamples for CO on a periodic basis. This cycling of the sensor is the source of its increased power demands. Detectors powered by batteries typically use a passive sensor technology which reacts to the prolonged exposure to carbon monoxide gas.


Are some types of detectors better than others? How do I select the best detector for me?

Regardless of the type of sensor used all detectors sold on the market today should conform to minimum sensitivity and alarm characteristics. These characteristics have been defined and are verified by Underwriters Laboratory in their standard for carbon monoxide detectors UL 2034. This standard was most recently revised in June of 1995 and went into effect in October of 1995. This revision specified additional requirements regarding identification of detector type, low-level (nuisance) alarm sensitivity and alarm silencing. Under no circumstances should one purchase a detector that is not UL listed.

Each of the two types of detectors mentioned previously has applications in the home along with associated advantages and disadvantages. The proper detector for each application or installation should be chosen based on the application requirements and the products specifications. The following are the principle advantages and disadvantages of the two different type detectors:



Characteristic           Household Current         Battery Operated       





Cost                     $30-50                    $30-50





Ease of Installation     More difficult- requires  Less difficult.  Can be


                         outlet near detector or   placed anywhere needed.


                         'hard wiring'.





Maintenance              No maintenance required   Requires periodic


                         during life of product    replacement of


                         (5-10 years). Detector    battery/sensor module


                         sensor becomes more       every 2-3 years at a


                         sensitive with age.       cost of ~$20.





Reaction Time/Exposure   Gives continuous display  Reaction time depends


Level Display            of CO levels updated      on concentration level


                         every few minutes.        and duration of


                                                   exposure.  Display


                                                   information is limited.





Reset Time               Will reset immediately    Reset time depends on


                         once CO problem is        exposure concentration


                         corrected.                and duration.  May


                                                   require removal of


                                                   sensor pack.  A silence


                                                   button, however, is now


                                                   provided/required.



How many carbon monoxide detectors should I have and where should I place them?

The Consumer Product Safety Commission recommends a detector on each floor of a residence. At a minimum, a single detector should be placed on each sleeping floor with an additional detector in the area of any major gas burning appliances such as a furnace or water heater. Installation in these areas ensures rapid detection of any potentially malfunctioning appliances and the ability to hear the alarm from all sleeping areas. In general, carbon monoxide detectors should be placed high (near the ceiling) for most effective use. Detectors should also not be placed within five feet of gas fueled appliances or near cooking or bathing areas. Consult the manufacturers installation instructions for proper placement of a detector within a given area.


What are the most common causes of carbon monoxide detector alarms?

There are many conditions which can cause a carbon monoxide detector to alarm. Most are preventable and few are actually life threatening. Ideally through proper placement of the detector and education of the users the number of preventable calls can be minimized and activation will only occur in the more serious situations.

Preventable causes of CO alarm activation and the recommended preventive action are as follows:



Cause                                Preventive Action                  





Inadequate fresh air venting of the  Have a heating contractor install a


home.                                fresh air makeup system in the home





Running gas powered equipment or     Gas powered equipment or vehicles


automobiles in a home or garage      should never be operated within a


                                     home or garage- even if the garage


                                     door is open.  Since most homes are


                                     typically at a lower pressure


                                     relative to outside air, the gas can


                                     actually be drawn into the home.





Charcoal grilling in the home or     Charcoal grilling is a tremendous


garage.                              producer of carbon monoxide gas.


                                     Charcoal grills should never be


                                     operated in the home.





Malfunctioning appliances or         All fuel burning appliances or


equipment in the home.               equipment in the home needs periodic


                                     inspection and preventive


                                     maintenance.  While all fuel burning


                                     appliances will produce some CO gas,


                                     regular preventive maintenance can


                                     keep this to a minimum.





Malfunctioning or overly sensitive   Buy only UL Listed alarms conforming


alarm.                               to the latest revision (June 1995)


                                     of UL standard 2034. This revision


                                     includes new requirements to minimize


                                     nuisance alarms.


While many causes can be prevented others can not and may occur unpredictably. Not only are these problems harder to predict but they also tend to be more serious in nature. Examples of these type problems are:

Minimizing preventable events allows everyone to take other less preventable and predictable events more seriously.


Where can I get further information concerning carbon monoxide detectors?

Several manufacturers of carbon monoxide detectors offer toll free numbers for additional information regarding their products. These numbers are as follows:



  Manufacturer                         Number           





  American Sensors                     800-387-4219





  Enzone                               800-448-0535





  First Alert                          800-323-9005





  Jameson                              800-779-1719





  Nighthawk                            800-880-6788





  Quantum                              800-432-5599





  Radio Shack                          Contact your local store





  S-Tech                               800-643-5377


Additional information with product ratings is contained in the July 1995 Consumer Reports issue on home safety products. One word of note regarding the ratings in this issue- the products tested have probably since be replaced by updated models conforming to the revised UL 2034 standard which took effect in October 1995. Check with the manufacturer for current information.

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