Probably a 'Pellistor' device. Basically two thermistors, one coated in a catalyst, the other not, heated, in a chamber open to the air to be sampled. When there is flammable gas present, the Pellistor with the catalytic coating gets hotter than the other one. The thermistors are arranged in opposite arms of a bridge and normally a self-balancing circuit (time constant several minutes or more) of high gain gives a pulse out when one thermistor takes the bridge out of balance.

Your pee will probably dry off if you flush the Pellistor with distilled water. Trouble is that the Pellistors are usually behind a sintered plate (Flameproof, eX) and the plate could get clogged. Still, leave in distilled water for some hours and leave to dry for a week or so. You have a good chance it working.