I got my parents a NetAtmo device it has an outside thermometer but also one for inside that also has a CO2 detector. It's amazing how often just my two parents

I got my parents a NetAtmo device it has an outside thermometer but also one for inside that also has a CO2 detector. It's amazing how often just my two parents plus one cat in a 5mx5m living room will cause it to reach near 1000ppm. At Christmas time with about eight people it easily hit 1000ppm very quickly. Nobody else knew but I was watching the readings and it was interesting to see how that point it seems stuffy so a window was opened for some fresh air. This is a 1970s single floor bungalow with forced air heating but no air exchange.