Adding a filament runout sensor?

So I was looking at the break down of all the board connections and one of them is for a filament sensor, now granted I understand that we have two extruders but I was wondering if we could still hook up one sensor for our main spool which is what I primarily use most as my second spool is used just for PVA for support interface, or if we can daisy chain both filament sensors into the one plug?

Now if the answer is yes to either of the two options mentioned above, then my next question would be will the firmware natively detect and support the sensor or would we have to compile new firmware?

Last option is there a standalone filament sensor that doesnt report to the board at but has like flashing led or an alarm when it detects that filament has ran out?