I figured out how to connect 4-wire (motion and smoke), normally open (smoke, fire sprinkler), and even old legacy wireless sensors (windows, heat) to the Ring Retrofit kit with just a simple two component resistor-NPN circuit. I made a video on Youtube. Click or search for “ring alarm retrofit with normally open” on youtube. This is not a simple project but if you’re handy with a soldering iron and have built a few circuits in your days then this tells you how to do it. I also give cautions on why you’re better off replacing smoke detectors with First Alert z-wave. But in my system I have other legacy devices I needed to support.