So, I have a Square D QO panel that had one of the original AFCI breakers go bad, and in the process of researching how to fix that, I learned a bit about this whole AFCI thing and how newer code requires it in virtually all living areas. After replacing the bad breaker (test button never worked), this means that only my bedrooms have AFCI protection via two breakers. I began to look at my living room setup and discovered that it's on a two-pole breaker (15A), with the second pole shared by the main hallway and bathroom lighting circuit, w/ both branch circuits sharing the neutral wire.
Some more digging turns up that Square D (now owned by Schneider-Electric) does not make a two-pole AFCI breaker for QO panels, citing limited demand for two-pole AFCI for shared neutral circuits (pg 6)†. So I looked up an AFCI receptacle, which are pretty new overall, and found the AFTR1-W by Leviton. If I were to get and install such a receptacle as the first living room receptacle downstream of the living room breaker, will that provide AFCI protection for all downstream receptacles? And will the neutral wire going through the the living room circuit cause the AFCI receptacle to trip if I flipped on the hallway or bathroom lights?
If so, that will cover about 98% of my living room outlets. Oddly enough, it appears that the builders pigtailed somewhere after the living room breaker, but before the first receptacle, and used that pigtail to power a GFCI receptacle by my front door that grants GFCI protection to the receptacle outside on the front of the house. I can test this, because if I plug a GFCI tester into the first downstream socket, I can't trip the nearby GFCI receptacle, so they have to be in parallel somehow.
I don't think that if I put the AFCI receptacle in that I'll be able to cover that GFCI receptacle as well, unless I find the pigtail in the wall and wire it to be on the load side of the AFCI receptacle somehow. But that's only assuming the shared neutral doesn't prohibit me from even using the AFCI receptacle. Also doesn't look like they make a combination AFCI and GFCI receptacle device, either.
† Also, Schneider-Electric has this to say about shared neutrals in residential wiring, too.