Use the Bluelab? External Lockout & Alarm Box to connect the Bluelab? Pro Controller to external switches, for example, a float switch or a greenhouse alarm system. When these switches are activated, the Bluelab? Pro Controller is placed in lock-out mode, so no further dosing will occur until reset. Comes with built-in alarm that can be disabled if required. It can be connected to an external alarm (horn or flashing light).