In the last dying gasps of this Ex-WSM Gold (hmmm... who could that be??) they did this bells only as a G2X. Full paperwork
not a homer or cash job etc...
To be honest I'm now (possibly) changing the panel just over a year later so haven't thoroughly investigated this little setup;
as its going to be changed for a DT and, hey, might just put a contact on at least one of the 2 external doors to the
area.
It's either wired as a 2 zones to get a confirm, or wouldn't be at all surprised if wired in series to cut down on FAs....
Remember the same brains behind it are still trading.....
If we get the job I'll let you know how it was wired.