Hi I am not sure if this is the correct forum to post this on, but I guess it can be moved if it is not. I just want to know what methods exists to detect gases in a room. Smoke alarms use ionization or electromagnetic light. What other technologies exist on the market? What technologies are used in detectors that are used to detect, for instance, radon gas? I know light is used to figure out the composition of gases in the atmosphere of distant planets. Is this practical in a room? Finally, are there any more theoretical ways of detecting gases? What books should I read to learn about this?