In an example implementation, a system includes a control module, one or more electric circuits, each electric circuit including a resistor and one or more notification devices in parallel, and a supervisor module electrically coupled to the control module and the electric circuits. The supervisor module is configured to receive input electric power, the input electric power having a voltage in a range of 12 to 16 VDC, and apply, to each electric circuit, first electric power having a first polarity and a voltage of approximately 12 VDC. The supervisor module is also configured to determine, based on electric power returning from each electric circuit, an operational state of each respective electric circuit, and receive, from the control module, a trigger signal indicative of an alarm event. The supervisor module is also configured to, responsive to receiving the trigger signal, apply, to at least one electric circuit, second electric power having a second polarity opposite the first polarity and a voltage of approximately 12 VDC.