*shakes his head* Unfortunately the wiring diagram will now be very simple, if I can do it at all. It'll be a straight circuit of 14-3 from the box to each smoke detector in succession.
I've a feeling you're asking about the wiring diagram of the smoke detector, and modifying it so that the neutral line from the alarm signal is routed through another wire, rather than shunting it off to the AC line's neutral. While I imagine this is very possible, I'll be using different alarms, and that's a bit more complicated than I plan to get in this upgrade. I like the thought though, considered it myself, if only very briefly.
Proby, aye. I'll add a notice to the OP to summarize the thread.
At this point I'm just going to see if I can run a line alongside a doorway to the stairs going down. I might be able to pull this off after all.
Technically, you don't need 14-3 from the breaker box to the "first" detector. There's no place for the red wire to connect in the breaker box.