As always this newsgroup comes through....Thanks for all the advice! I won't be attempting to interface the system now, and I'm going to try to convert the whole system over to 12v Napco FW-4W detectors, probably just capping off the 110 wiring outside the existing boxes, and diconnecting it at the main panel. Lot more work, but I really want the smokes to be monitored, so looks like that's my only safe option.
Thanks Again to All who provided advice!
If you're going to go to the trouble of bringing wires to each location anyway ....... why wouldn't you just leave the existing smoke detectors operating and install the low voltage units "outside the existing box"?
Having both kinds of smoke detection is certainly better than just one.
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