The Simplex 4098-9788 is a 2-wire conventional detector base. It belongs to the Simplex TrueAlarm product line. Specifically, it connects 4098-series photoelectric heads to a conventional Initiating Device Circuit (IDC).

First, the base provides a simple plug-in mount for the sensor head. Then, the head signals an alarm by drawing current on the same two wires that power it. As a result, no separate signal pair is needed. Therefore, the wiring stays simple for retrofits and small layouts.