nokia auto-dialer

[scuder]

I want to use a nokia phone to auto dial another mobile on an alarm activation, when i was a uni i shared a flat with an electronics student we got broken into a few times so when the house alarm went off he made it so the 12v activation of the siren activated via the ear phone wire to auto dial the last number in the phone it worked brilliantly, all as i can remember was two wires from the alarm (12v) went into a small matchbox couple of componants into nokia via ear pice and it rang the last number dialed automatically
,brilliant

anybody know how to do it or have a circuit i could knock up, or know of an easier way would be appreciated