OK I'll declare this issue solved. 3 days later and the alarm hasn't played up. Removing the backup battery from the siren solved the issue.
Just to summarise for other people who might encounter this problem: -Alarm going off randomly - possibly sounding broken/quiet.
-If you can still unlock and start the engine with the alarm sounding - this is an alarm siren malfunction, likely due to a failed backup battery.
-open the siren, possibly mounted near the car battery and remove the small backup battery.
Thanks KHLow2008 for your suggestions.
Monday, March 26th, 2012 AT 9:11 AM