Some Alarms don't like heat - if it's really hot in the car it might go off... Other than that, check all the switches are working right - doors, boot bonnet etc... Some alarms have a diagnostic to tell you which sensor was triggered (mine used to beep 4 times for the bonnet, 5 for the doors, 6 for the ultrasonics) - maybe yours has that? Other than that take it to an auto electrician I reckon!
