Thanks 'Marlon' for letting me know about the whereabouts of the '155 technical centre' in its absence i'll post on here because i guess an early 156 might experience similar problems!!
The car is a 1997 155 2 litre ts sports, i went to get in it on saturday, only to find the remote central locking won't work, so i opened the door from the key slot on the drivers side. This immediately set off the alarm, which i'm guessing is the volumetric sensor kicking in. I read the maunal and found out how to switch the alarm off by using the emergency key in the glove box, but it didn't work! SO what is the problem?, the battery in the key isn't flat because the little led lights up, so i'm thinking its the sensor inside the car thats the problem, can these be easily fixed? or is there a way of cutting the alarm out temporarly under the bonnet?. The engine still starts which must mean the imboliser switches on and off ok. I need to fix it asap as i'm moving house on friday!