If you don't want to go the DIY route, and also are interested in a weather station, Ambient Weather is great. It just works out of the box (the CO2 sensor is

If you don't want to go the DIY route, and also are interested in a weather station, Ambient Weather is great. It just works out of the box (the CO2 sensor is an add on), and supports a large pile of local APIs and cloud service integrations. We went with one of the fancier models, including a nice LCD display and a solid state (ultrasonic) wind monitor, since we get hurricane-level gusts around here. It's held up fine so far. One annoyance: At least the last time I checked, all the sensors have to be in radio range of the base station. It'd be nice if they had WiFi bridges so we could monitor multiple buildings, etc, with one system.