1) Faulty micro switch in door module or washer leak into boot catch? Car then thinks door/boot has been opened
2) I'm pretty sure error codes are stored indicating why the alarm went off recently
3) Get a cable off ebay etc, then try sweet talk someone on here for a copy of VAGCOM
If all else fails, try inhibiting the alarm with the switch at the bottom of pillar behind driver's seat, until you can get it scanned