Airgradient's popular indoor air quality sensors are the first devices of their kind to be officially certified as "Works with Home Assistant". These open-source devices do not require an internet connection and enable local automation with air purifiers, air conditioners, or humidifiers and dehumidifiers.
CO2 concentration is an indicator of indoor air quality and can generally inform the quality of ventilation. Indoor plants likely won’t exchange enough to be effective.
Baseline (outdoor) is around 400 ppm, 1000 ppm is generally the ‘comfort limit’ or where some cognitive effects start to become present (drowsiness), then over 2000 ppm is generally the unhealthy limit.