Hopefully someone can help.

I am putting in a new alarm and have a particular problem with cabling for motion sensors in two upstairs rooms and the installation of an indoor siren on the top floor. 

The problem arises because there is only a single 6 core cable running from the control box downstairs and up into the attic.  There are then two 4 core cables that run down from the attic into the two rooms.  This easily allows me to set up the two rooms as separate zones.

However, I also want to put in an internal siren in the ceiling of the upper floor. If I had another cable from the control box up into the attic, then it would be simple.  However, I haven’t and it would be very difficult to put one in.

I believe that it is still possible to put in the siren as well as having two separate zones for the two sensors using the single 6 core cable that runs to the attic.  I think that this involves using the pgm outputs on the DSC and using relays in the control box.  However, I don’t know how to do this.

Can anyone help, ideally with diagrams etc.

If it can’t be done, then the alternative would be to put the two sensors in series and only have one zone, but my preference is to have each room as a separate zone.