The FPC-500 Series Smokes are 4 -Wire technology, but if using more than one FCA-500 on the same loop it is a 6 wire configuration: 2 wires for power, 2 wires for the trouble loop, 2 wires for the alarm loop, and the last base on the loop needs to be a FCA-500-E (End of Line Base).
If using only one smoke or installing them on and addressable loop the FCA-500-E base is required. The wiring configuration is, 2 wires for power and 2 wires for the alarm loop. Then for the trouble circuit you wire a jumper from terminal (T1) to terminal (b1/b2).
Note: The last base on each loop of flush mount smoke detectors must be a FCA-500-E - Wiring is 4 conductor from the panel to the first head and 6 wires between the first base in the loop to the FCA-500-E base at the end of the loop.