Laguna car alarm problem

I have a 2003 Renault Laguna. The car alarm did not come as standard but was installed by the first owner after purchase. Very annoyingly, to me and my neighbours, the alarm now goes off frequently, typically when another car drives past it. (I have to park in the street.) Non-main dealer car service people tell me they're not allowed to touch it and i have to go to a main dealer. The main dealer quotes £50 just to look at it with no guarantee of fixing it. Rather than invest loads of money in fiddling about with it, I'd rather just disconnect it. However, the main dealer said 1st they weren't allowed to, then said they could but it would cost £100. How can it cost a £100 to disconnect something. All it needs is for the thing that actually makes the noise to be disconnected. You wouldn't have thought it would take 3 minutes. Anyway, they've now gone back to saying they're not allowed to do it .

Any advice anyone?

Yours frustratedly

Andy

be carefull with the dealer,my laguna had a faulty alarm,dealer said it would cost £100 to fix.once they had the car it was more like £600.and i have found out these alarms are a common fault on the phaze 2 laguna