We have had since new, a '92 passat, 4, GL, that in the past several years has set off it's theft alarm all by itself nearly a dozen times. Often this is very embarrassing as it may happen in traffic, on the highway or sitting at a stop light, always with out warning or provacation. We have learned to just ignore it and smile at people when they gawk at us merrily driving along with the "horn" blaring. it will stop on it's own volition after about 4 minutes. The owners' s manual from Bentley, I think it is, has nothing about trouble shooting this particular problem. I can't even find where the alarm horn (it's not the regular horn-I can find that one) is to yank the wires out of it.
Any one had the same problem and been able to fix or disable the alram?

try beneath the windscreen scuttle in engine bay