Have you tried the schoolboy error stuff first in trying to find out what is setting it off?
A lot of alarms with ultrasonic detectors inside the cabin, do not like open air vents as sometimes an inrush of air has been known to set these off, it is sometimes better to change these to volumetric ones.
Also dangling air freshners or other silly decorations in the car can set the sensors off by moving if the car has been moved or rocked by a strong breeze or wind, so this will then be picked up as movement by the alarm.
Also check the courtesy light in the cabin and the boot are actually switching off as failure to do so will set off the voltdrop trigger of the alarm. Also take a look at the bonnet switch for the alarm and make sure that it is operating properly and that the connections are not corroded.
And finally, is the alarm self powered ie. does it have a built in battery which still allows the alarm to sound should the main battery lead be cut? If the main battery has a problem cell then this too can fool the alarm into thinking that there is a voltdrop trigger and sound the alarm. Check the main alarm unit itself and see if it has a small adjustable screw under a rubber bung, this is sometimes the vibration trigger depending on the model and sometimes can be set too sensitive. If it is there then adjust the screw slowly in stages both clockwise and anticlockwise, turn on the alarm and rock the car or kick the tyres until it goes off and then readjust accordingly to reduce it's sensitivity.
I hope this helps, good luck buddy
