Does anyone know of a reliable and cheap CO2 monitor (other data about air quality is not needed) for a music room that will be kept almost tight closed with potentially more than 1 person playing music? I need to know when levels will rise above normal so that we can stop and take a pause to exchange air. I've done some research and found complains about fake products coming from the usual suspects, some of which use alcohol sensors disguised as CO2 ones, which of course don't work. I've taken DIY into consideration, then again discovered they sell fake parts too, like some MH-Z19 modules found on Ali* and elsewhere.