I employ many types of direct reading instruments in my profession. CO sensors are available in three basic flavors: electrochemical, metal oxide, and colorimetric. Each have positive and negative characteristics. ALL direct reading instruments, by their very nature of ingesting the target atmosphere, suffer from degradation due to ambient temperature, humidity, and possibly the target compound.
You would think that the manufacturers are holding nuclear secrets when trying to get a simple and straight answer as to the sensor type provided. All I can get from the manufacturers of “marine” units is that their units “better resist the adverse effects of temperature and humidity.” Better than what? I don’t think it’s the sensor type. On my boat I use reasonable quality “home” CO detectors and swap them out every couple of years or at the first sign of erratic behavior.
For all types of CO detectors, any gas of similar molecular size and chemical reactivity can produce a false positive (alarm). Common CO detector interferents include acetylene, dimethyl sulfide, alcohols (ethyl, isopropyl, methyl), ethylene, hydrogen cyanide, hydrogen sulfide, mercaptan, propane, nitrogen dioxide, sulfur dioxide, and probably some others.
