Optima XM?

I have turned all power off in my house to fit some new lights, disabled back up battery and the alarm still goes off. Even disabled the fuses to the rooms that I am working in, alarm still goes off. I think someone has done a botch job of wiring it in before we moved in.

Does anyone know how to minimze length of time alarm goes off when activated (i was thinking it might stop after 15 mins...well hoping). Or do I have to go up a ladder to the main box outside and disable a fuse up there (last resort, I was hoping).

Any advice would be much appreciated. I was hoping to get these up before Christmas, ho ho ho.