An electrical control system is disclosed for controlling a plurality of variable transmittance windows. The electrical control system of the present invention comprises a master control circuit for supplying control signals representing transmittance levels for the variable transmission windows, and a plurality of window control circuits coupled to each of the master control circuit. Because the window control circuits can sense abnormal load conditions in the variable transmission windows, the system further includes an interface to a security system to inform of a potential intrusion. Each window control circuit controls the transmittance of at least one of the variable transmission windows in response to control signals received from the master control circuit.