Thanks Jason for the hint, Now I feel dumb as I had read on the guide
“An on-board siren relay is included for added convenience when setting up a hardwired siren, 60VDC/1A Max drives siren or other device” I then just assumed that the relay would be wireless driven 
But from what your saying above and your comments here that I could wire the 16s in as a wired relay and then it would work ?
Using this method ?
In the future I want to drive an external siren and maybe just thinking about retiring 16s ? and then to just use a relay like the Altronix RBSNTTL . At the moment its all just wired on my kitchen table so its easy to design it.