Some CO detectors will go off in the presence of another gas. This is called interference. This occurs a lot in chemical testing and in machines that are designed to test for gases in the atmosphere.

I'll bet that if you read the CO detectors manual you will find that H2 gas or H2S is an interferant gas.

I am not really sure what detection principle is used in your Carbonmonoxide Detector or I would be able to give you more information.

I worked for many years in the air pollution control field and have had special USEPA training in measuring atmospheric gases.

I can tell you that there are significant difference between CO and H2 gaes. H2 is much ligher and rises. CO is denser than air and will setting in low spots. H2S or Hydrogen Sulfide can damage some CO detectors.

Many Chemical tests have to eliminate the interferences before the testing can be performed. If that can't be done then a speical test is performed to take into consideration the interferance gas or compound.

Regards,

Moose1am