timmmay:
@Daynger I think wired in would make sense. Our Bosch alarm has one in the hallway and two channels free, which is good, but I'd really want three or four. I might talk to the alarm company. I don't have it monitored any more, wasn't worth the money for us.
You can wire them in parallel and daisychain more than one smoke detector off the alarm zone, if running low on zones ill divide the house up into areas for smokes or run all of the smokes off one zone, it only makes it harder for fault finding. One resistor per circuit and you cant zone double any smoke zones as they work on a NO going closed circuit as opposed to a NC going open for normal zones.