Fike devices are all wired in parallel* the bases have 4 terminals.
Zone +ve (in and out)
Ov (-ve in and out)
scrn (Common screen/earth)
rem led (Remote led)
The last device should have its End Of Line Switch "on" (Which it will already have if it's a working system, do NOT connect the earth/screen to anything other than the device base scrn terminal.)
As they are all "Multi sensor" you can set them to be smoke, heat or mixture
*The interfaces are wired slightly different.