Had this kind of
problem on a 52 plate Passat Estate we owned before the Altea,at first it was the bonnet switch but the showed as being open on the dash
Fixed that by replacing it,its just a microswitch,but then the alarm would periodically go off,showed no fault codes,
On the Passat forum it was found that the rear washer tube was leaking onto the switch,they dont like being wet
Its worth spraying all locks and switches with WD40 or similar occasionaly