Comment by originalvichy

Ruuvi Air is perhaps the most open source device I've seen that measures CO2 etc. and is not set up to be an online device. The company itself (Ruuvi) does pretty much all their development in the open, and the Ruuvi Air sensor is the same. Uses a pretty high quality sensor module that includes actual CO2 and PM among others. I went for it after buying a cheaper sensor that only had a cheap sensor and algorithm based estimate of CO2, not a real measurement. Additionally it required an app so it was already a headache. Ruuvi Air only uses BLE so it shouldn't be able to send anything outside your BT range. The iOS/Android companion apps only include local push alerts when a measurement crosses over your set threshold.