How can I stop the alam sounding?

I have an accenta 8 intruder alsrm. I accidently cut through the cable leading to the siren and the siren went off. I tried everything to stop it (TAking fuse out etc) but it would not stop. I re-joined the cut cable and after swithcing the power off and on again the alarm stopped.
I need to cut the cable again to re-route it but do not want the siren to keep sounding whilst the cable is cut.
How can i stop this happening again?
Thanks