Shelly Plus Add-on is a sensor interface with multiple inputs for temperature and humidity sensors. It collects the data and displays it in real time in the app (sensors sold separately). Because a sauna cabin reaches high temperatures, automations keep control safe: if the heater exceeds a threshold, it switches off; or you get a notification when the target temperature is reached so you can start your sauna session right away.
Placement tip: mount sensors 20–30 cm below the ceiling, but not directly above the heater. Alternatively, place them on the wall opposite the heater, away from vents or cold surfaces. A second sensor at seating height improves accuracy.