Alfa Romeo Repair: Alfa 147 alarm - how to disconnect, horn logic, car thief

Question
Its actually a siren rather then a horn alarm, we can't find the system (neither can the AA.) I actually disconnected the battery last night which seemed to work, although I would have thought the alarm is powered by its own system (maybe I just got lucky!)
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-----Question-----
Hi - My alarm kept going off last night at 3am  and wouldnt stop, know matter what I did, just kept going. It cant be looked at until Friday, how do I manually shut off the system so that the same thing doesnt happen tonight? It would save my life for a quick answer.
-----Answer-----
a quick and easy fix is to disconnect the wires at the sounding device (the horn? easy to find the wires at the horn).

Answer
Logic would indicate that a security system have its own power. But, on automobiles this is rarely the case. In my experience, a separate siren is located somewhere in the engine compartment. It might be buried behind a headlight or in the fender well.  

I am not impressed with production security systems. If you are worried about theft--put a switch inline with the coil and  locate that switch where you please out of sight. An experienced car thief does not have time to search out the unusual.