I was looking at this same problem. Why can't I just get a micro module (any type) and connect sense wire 1 of the micro module to the alarm light bulb (it's 120vac). Power for the micro module is readily available from the line in to the septic controller. I suspect that the sense wires draw little to no power, so this should work. I suppose I could connect the sense wire to the buzzer circuit, which would certainly have enough oompf to drive the sensor wire of the micro module. Once connected, I can just monitor the state of the module with the ISY. Since the Insteon modules are dual band, it should work even inside a metal enclosure. No batteries and no relay required.