WhisperGreen Select™ condensation sensor plug 'N play module helps control bathroom condensation to prevent mold and mildew. Sensor technology detects relative humidity and temperature to anticipate dew point, automatically turning the fan on to control humidity. Built-in relative humidity (RH) sensitivity adjustment enables fine tuning for moist conditions and for satisfying CALGreen requirements. When the condensation sensor is used in conjunction with multi-speed functionality, the fan will ramp up to high speed when the condensation sensor detects moisture in the room. This module also activates a 20 min delay Off timer for the fan. Panasonic WhisperGreen Select™ Condensation Sensor, Plug and Play, For Use With: WhisperGreen Select™ Series Ventilation Fan, Steel, Galvanized, Import