Review on High-Quality Digital Temperature Humidity Monitor - 9999ppm by Larry Morris

A must-have tool during a pandemic to ensure proper room ventilation. I'm glad I bought this; My tightly sealed house had 1600ppm of CO2 and this meter clearly shows when the windows have been open long enough to bring CO2 levels down to a more healthy 600-800ppm. Buy this if you want to look like a contractor. It's huge and yellow, but actually light, especially for its size. The C02 value appears 30 seconds after the countdown; The initial indoor relative humidity after the unit is placed outdoors takes some time to stabilize, maybe ten or 15 minutes. Toggling between air temperature, wet bulb, and dew point is nice; I wish it would show the heat index as well. Now for the bad: terrible design with human error; without a guide you will never get the hang of it - thank goodness the little guide explains everything pretty well. Don't lose the instructions. The keys clatter so much that sometimes a key press is not recognized. RS232 interface? Stone Age technology and forget about using your phone to log data. An alarm initially set at 1000 PPM is probably not a good choice; If you take this to your local grocery store, neighborhood bar, school, or work and take measurements that exceed that strict limit, you'll spook everyone. It's easy to replace (but don't forget the instructions). I would buy it again. It works well. I like it.