A Medical Mystery

Recently, my father bought a Portable Combustible Gas Leak Detector so he could check for leaks in one of his rent houses. Because my dad is a curious man, forever wondering about things, he blew into the flexible probe and was immediately surprised by the alarm going off. In fact the level of combustible gas in the air coming out of his lungs was over the top level. All the lights were on and the static-sounding alert went crazy. Perplexed, he took the machine home and asked others to try to set it off. Nobody could get even a crackle out of it or a flash of light.

Since Dad's been having gastrointestinal issues for some time, he had a doctor's visit scheduled for the following Monday. Carrying the device into the office, he showed the internist what happens every time he blows into it:  alarms go off.  The nurses in the office all blew into it with no effect. The doctor didn't know what was going on.  So I'm asking for help. Does anyone out there know what this might mean? I've seen a couple of possibilities, but I'd really appreciate more suggestions, since this might be very beneficial in solving his health issues.

Here is a list of the gases measured by the device: Acetone, Acetylene, Benzene, Butane, Ethanol, Ethylene Oxide, Gasoline, Hexane, Hydrogen, Industrial Solvents, Methane, Paint Thinners, Propane, Natural Gas, and Naptha.