Extracts from thread on Carbon Monoxide monitors from IAQ YAHOO GROUPS

First, ANYTIME you are “Discussing” a Nighthawk CO Unit, it is Important to KNOW the DATE of MANUFACTURE ! ! !

IF it was PRIOR to October, 1998, … 99 times out of 100, IT WILL BE A MOS Sensor, …..which offers OVER 2,000 possible “Cross Sensitivity” Possibilities. [Once again I refer you to the GRI Final Report of 1999 / 2,000].

Second, “ROASTING” ANYTHING ORGANIC …… is a Moderate form of “Burning”, which causes Molecular Change, which produces “Fumes, and / or, Gases”, as well as INCREASED HUMIDITY in the Immediate Area.

Therefore, just as a piece of plastic that gets HOT Enough to WARP, produces enough GASES to set off a GAS/CO Detector, ….. ANYTHING that is being “ROASTED” … “COULD” cause CO Readings.
If it involves a MOS Sensor, … the INCREASE of HUMIDITY ALONE can Cause an Increased Reading. Add the factors of the SUPER-SENSITIVITY of MOS Sensors as they “AGE”, … and the “Plugged-UP’ Filters, … and “FALSE”  / “NUISANCE” ALARMS are VIRTUALLY GUARANTEED  ! ! !
In my opinion, the #1 CAUSE of CO Detector/Alarm PROBLEMS, “False / Nuisance” Alarms, … and “False Negatives” [Failure to Alarm when they SHOULD], are a RESULT of HUMIDITY CONDITIONS. BOTH MOS and COLOR METRIC SENSORS are VERY


Obviously, the “FAILURE to ALARM” in LOW HUMIDITY Conditions is a FAR GREATER PROBLEM, … and has PROVEN to be TRUE with both of the MOS and Color Metric Sensors used in CO Detectors / Alarms.
Add these Facts to the Manufacturer’s OWN STATEMENTS, such as:
  • First Alert Model FCD4, on page #19 of its Owner’s Manual states: “DISPLAY ACCURACY”: “Accuracy is +100% -40% of actual concentration of CO at 50%RH+/-5%RH and 73F+/-4F [23+/-2C].
  • ALL Nighthawk MOS Sensor Products using the MOS Sensor Technology State that they are Accurate: Plus, or Minus 40%, PLUS 15 PPM [parts per million].

Most of these units were Manufactured prior to Oct. 1998; however, Many have been purchased since that date, … and Millions upon Millions are STILL in use throughout the World.


In October, 1998, Kidde/Nighthawk introduced their Version of an Electrochemical Sensor, [not the “Industrial”, Acid Based, used in Professional Instruments], and was Promptly faced with a Million Unit [1,000,000] RECALL, with 650,000 of these being their NEW SENSOR, and 350,000 being their “LifeSaver” Brand, Color Metric SENSORS.
The PRESENT Nighthawk CO Alarm Owner’s Manual on their Top of the Line, Electric with battery Backup Units State that the Digital Display is Accurate: Plus, or Minus 20% plus 15 PPM; however, NOT at Low Levels or on peak recall, and under Specific Conditions, with an Un-Contaminated Sensor.
All  UL-2034/CSA-6.19 Listed CO Alarms Packaging has the following, or Very Similar Warning:
It is NOT designed to measure CO Levels in compliance with Occupational Safety and Health Administration [OSHA] commercial or industrial standards. Also that many individuals need to seek a DIFFERENT DEVICE.
Nighthawk’s actual statement is:
“Pregnant women, infants, children, senior citizens, persons with heart or respiratory problems, and smokers may experience symptoms at lower levels of exposure than noted. Individuals with medical problems may consider using warning devices which provide audible and visual signals for carbon monoxide concentrations under 30 ppm.”
Regards, …………………… George


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