The F950-650 XP95A Smoke Detector is de-signed to be connected to a two wire loop circuit carrying both data and a 17V to 28V DC supply.The detector is connected to the incoming and outgoing supply via terminals L1 & L2 in the mounting base. A remote LED indicator maybe connected between the +R & -R terminals. This detector is a direct replacement for the F900-650 Addressable Photoelectric Smoke Detector.