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 which can be disabled if required. It can be connected to an external alarm (horn or flashing light).