The following picture shows you some of the Sensors being used in products you may have in your house.



1. The First Alert Sensor is a Very inexpensive version of a MOS type Sensor. In the Owner’s Manual for this product (Model # FCD4), on page #19 it says that this Sensor is Accurate to: “Plus 100%, … Minus 40%. [GRI Testing found it well over 100%]2. The Nighthawk Sensor is a “Water-Based” Electrochemical Sensor. The Owner’s Manual for this unit says that it is Accurate to: “Plus, or Minus 20%, but not at Lower Levels”. [GRI Testing indicates 40% plus.]

3. The AIM, Senco, SF, and CO-Experts Sensors are All Acid Based Electrochemical Sensors, [Like those used in Industrial / Hazmat Meters].

The SF unit made to North American Standards has No Digital Display; therefore, No Accuracy is stated.  AIM did NOT make an Accuracy Claim; however, [GRI Testing found that it was within Plus, or Minus 10%.].  Senco claims plus, or Minus 20%.[GRI Testing found 40%+]CO-Experts is Accurate to One PPM, [Max. Error 10% at 50 ppm, prior to “Err” Warning.] [ It is NEW, was not available when GRI Testing was done.]

Please *Note the Larger Volume of the CO-Experts Sensor, and the fact that the necessary “Filters” on the Nighthawk Sensor were “Shrink-Wrapped” over the end of this Sensor following the 1999 Recall of 650,000 of this type of Sensor.


GRI, [Gas Research Institute], collected and documented a large volume of Reports on CO Detector / Alarm “Responses” to C O Alarm activations over the years 1994-99. Among the many items covered in these Reports was the “TYPE” of Sensor Technology used in the CO Alarms that resulted in the CO Responders Investigation.

The following Chart indicates Very Clearly, that as the “Average Age” of the CO Alarms in our Nations Homes Increases, … so does the “Percentage” of these “Un-wanted / Nuisance” Alarms that are using a MOS, [Metal Oxide Semi-conductor], type of Sensor.

The scope of this Problem will continue to Increase EVERY DAY until these products are REMOVED from the homes in our Nation.

NFPA 720, Guidelines on the Installation and Maintenance of C O Alarms says that C O Sensors are to be Calibration Certified, [Checked], every three years. Since this is NOT practical in the case of “Residential Single Station C O Alarms”, it is the recommendation of C O – Experts that ALL Residential Detection / Alarm Products should be REQUIRED to have an Automatic “Kill Switch” installed to indicate the    “End of Useful Life”, … WELL BEFORE this Excessive Nuisance Alarm age is reached.




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CO Experts

19299 Katrina Lane; Eldridge Missouri 65463-9102

Tel: 1-888-443-5377 Fax: 1-888-436-5377