Looking for some clarification on smoke wiring - 1 family residential. Have 6 smokes/CO all hardwired /interconnected using 3 wire. These will be added to general lighting circuit, hallway lights, etc. as long as they're interconnected, it does not matter where in the series I draw from the gen light circuit that will be feeding them, correct? 1st, 2nd floor or basement, wherever the closest line is on that circuit? Thanks

Not sure if I understand exactly your question, you can feed the first detector with 120 volts, black white and ground, and then run three wire to each detector, in any fashion, series , tee tap, in any order, as long as the blacks, reds, and whites connect together at every detector.

Does this help?

Answers it perfectly, thanks. Actually 1 follow up - some of these smokes went into old-work locations, and I used the plastic remodel boxes. SDs don't have grounds, neither do the boxes. What to do with the ground - simply tuck it up into the box, put it on the mounting screw for the SD?

I always, due to habit, splice the grounds, for continuity, and cap with a wirenut, and just fold them in the box, as if they would be used in the future.

No need to connect to any screw, the SD and box is plastic.

But, say in the future, someone comes along and adds one and uses a metal box, the ground is all set, ground wire will need to attach to the new metal box to ground that.