The SmartExhaust is designed as a replacement for the bathroom fan and light switch, helping insure healthy indoor air quality as well as adequate bathroom ventilation. This version has the Decora or Rocker switch. By using a microprocessor to monitor and control fan operation, a precise amount of ventilation can be provided.There are two settings on the SmartExhaust switch, ventilation and delay. Ventilation is the minutes per hour that you want the fan to operate. Delay is the number of minutes you want the fan to run after the bathroom light has been turned off.The delay time provides additional run time of the fan to complete ventilating the bathroom after use. When a person enters the bathroom and turns on the light, the fan is also energized. After the person leaves the bathroom and turns the light out, the fan continues to run for the set delay time. In addition once an hour the fan is energized for the set ventilation time. What makes this switch particularly unique is that the microprocessor monitors manual operation time and Delay time and subtracts it from the set hourly ventilation time.