Whether arc-fault protection is required depends on which NEC you're using. Here in Va., we're still on the '99 code, which requires arc-fault protection on only the receptacles, not all outlets like the '02 code requires.
I imagine that any wired interconnecting scheme would require pre-wiring at least as complicated as running 3-conductor cable, might not be UL-approved, and/or may require a difficult approval procedure.
I just finished roughing a house with 14 detectors (over 7K sq.ft.), and fed them their own circuit, using 14-3 from the first detector on. Being on another circuit didn't come up at inspection. They will of course be battery-backup units.
If anyone is interested, I do have access to a wireless detector-interconnect system. I believe it's a power-line-carrier link (similar to X-10, but not X-10). The individual detectors do not have to share the same circuit.
Larry
[This message has been edited by Larry Fine (edited 04-24-2005).]
