The SRT02 Thermometer is powered by light and light on the planet. It can be used both indoors and outdoors to monitor the temperature, as well as displays the high and low of the day. The built-in solar panel powers this thermometer by using energy from the sun or ambient light. The suction cup can be switched from front to back (or back to front) to suit your situation. Like this model? Also check out our indoor solar thermometer SRT01!