Emerson F145-1378 Outdoor Remote Sensor Designed for sensing temperature remotely when the thermostat is installed in a different room or poor temperature sensing location 12 ft. sensor lead Compatible withEmerson Blue and White-Rodgers thermostats that have the wiredoutdoor remote sensor option Dimensions: 2-1/8" x 3-1/2" x 3/4" No temperature variance caused by wire resistance