With this built-in feature, there is no need for an additional manual bypass switch when using rain sensors (the Pro-C works with the Hunter Mini-Clik®, plus some other rain, wind, and freeze sensors on the market today). If the system is preventing system operation (or no sensor is installed and the switch is in the ACTIVE position), SENSOR OFF will be displayed. Simply move the switch to BYPASS and the weather sensor will be bypassed. This allows you to use the system.