To turn on the nGauge 4x4 Temperature Sensor, unscrew the top and locate the power button. Press and hold this button for at least 5 seconds and wait 1 minute before trying again if needed. You should start receiving updates in the app. Screw the lid back on tightly. Use the provided fasteners to secure the sensor to the basket or lid of your fridge or freezer. The sensor is waterproof, however complete submersion should be avoided.