Deas - it was serviced over a year ago and there wasn't any problem with the sensors, in fact the battery on the front door was replaced. We are very careful to close that door properly and gently so it can't be that the door is not closing properly.
Emeralds- maybe....... I read before that this type of thing might happen.....
AlbacoreA - No, there wasn't any repair done, see my OP, I didn't call for the service. As soon as I mentioned that I would get a service engineer, the false alarms mysteriously stopped!!