Air sensors

Most ventilation units measure a supply temperature and nothing else — no humidity, and CO₂ almost never. Link an external sensor to a unit and the app reads the air from it: the air-quality score works, auto-boost finally has something to trigger on, and the advisor has something to advise about. Four ways in. A Shelly H&T or Plus H&T is read over the local network by its address. Netatmo and Aqara are accounts — sign in once with the credentials from their developer page and every sensor on the account is added at once. Anything else that answers with JSON — Home Assistant, Zigbee2MQTT, ESPHome, a Homebridge plugin — is the fourth: give it the URL and say which field holds the reading. The unit always wins where it can measure for itself. A machine reading its own extract air is reading the air it is actually moving; the sensor fills the gaps, and the card says when a figure came from it.