Oregon Scientific THN138 is a Remote Thermo Sensor designed to work with compatible units like the 433MHz Multi-Channel In-Out Thermometer to monitor temperature changes in outdoor areas. It eliminates the need for wired installations and provides convenience in temperature monitoring. With its weatherproof design, it can be placed outdoors, shielded from direct sunlight, rain, or snow, making it suitable for various monitoring purposes. The sensor features three channels, allowing you to use up to three sensors with a single main unit.