My woman was driving home lastnight in the AU3 xr8 and all of a sudden the alarm went off! she turned the car off, hopped out, put alarm on then turned it off and tried starting it again but the alarm would go off once it started. I went out and drove it back home with the alarm going off (lucky it was only 5 minutes away) and then it just stopped half way.
I had a look at it and noticed that the box was lose and moving around. could that be the cause of the problem or could it be wiring?

check out the earth wire.
the box being loose wouldnt be doin you any favours id secure the box then see how it goes.

Is the whole alarm going off? As in the lights are flashing too.

If it's just the siren, it means it has been disconnected from power, so check the wiring for it.

Battery backup sirens go off when they are unplugged.

its just the siren going off. i started the car and it was going alright for a few seconds untill i closed the bonnet then the siren went off so I gave the box a bit of a wiggle and the siren was going on and off. ill tighten it up tomorrow and check the wires.
thanks for the help fellas!