Dew Point & Mould Guard

The dew point of every room, and the risk that water condenses on its coldest wall. You pair an indoor temperature and humidity sensor, you add an outdoor temperature, and the app tells you in degrees how much margin is left before the wall gets wet. The app reads no outside data: everything is computed locally, from your own sensors, using the Magnus-Tetens formula. Nothing leaves your home. It asks for full access to Homey for one reason only, that the SDK offers no other way to read sensors owned by other apps. The cold wall estimate only holds when it is colder outside than inside, and the app says so the rest of the time.