re: Carbon monoxide/explosive gas detector- anyone use this?

Normally these are confined space monitors. They are programmed to go off at a certain thresh hold, which is before lethal levels of either are reached. You keep it clipped to your belt, or if going down in a hole they also offer monitors with a probe that you can drop down to get a reading. Industrial Scientific and MSA both make very reliable monitors.

Eta: are you talking home use or field use? I believe I misunderstood the question.