You can wear the sensor in the sauna, but we do not recommend it as the sensor can fall off more easily if your skin is sweaty. The temperature range specified by the manufacturer is between 10 °C and 45 °C. 

Please note that no readings may be recorded as the sensor can switch itself off if the temperature is too high. However, it will switch itself back on when it returns to normal temperatures. You may also see an incorrect peak value during a sauna session.