The PESM (Programmable Energy Saver Module) is used to override existing thermostats for set-back control. It can also be used for sensing and controlling other temperatures, such as attic fans, garage fans, greenhouses, basements, wine coolers, humidors, etc. Can also be used to control spa heaters with remote temperature sensor. The PESM reports temperatures to the controller, and has a low voltage relay and LED indicator for control. The PESM doubles as a freeze sensor, which can cause the controller to dial out in the event of a furnace failure.