Hi Brain,

Generally you can leave the sensor outside in the winter. However, if the temperature goes below 0°F(-18°C ), you should consider taking the sensor inside. Please turn off the sensor before storing it. To turn off the sensor:
1. If the sensor is powered on (the light is on), press the button once to turn it off
2. If the sensor is sleeping (it will wake up repeating to report data), press the button once to manually wake it up, wait for  2-10 seconds, press the button again to turn it off. 
3. After that, the sensor will stay off and will not wake up repeating to report data

If you place the sensor in a place without any sunlight, after a few months you might need to charge the sensor for a few days before it can turn on.

Thanks,

Netro Support