Has anyone had problems with a Serpi Star alarm going off on their Fiat Ducato 14 swb N-reg (1995 iirc) -based motorhome?

I've had an auto electrician out to have a look and I've done what he's advised - cleaned the bonnet switch and moved the magnet near the reed switch on the habitation door.

I also need to get a new battery for the fob as that appears to have suddenly died - pressing the single red button on the fob doesn't light up the red led atm.

The last time the alarm went off was 4.30am a couple of days ago and it was frustrating turning it off. The fob didn't work and the cab battery was getting charged. I then went in via the habitation door and there was no change to the alarm, no flashing indicators, just a siren. It wasn't until I faffed around putting the 'master' key in and turning the ignition on that the alarm eventually subsided. I guess it eventually gave in after reading the code from the key - it took a couple of tries!

I think there are two alarms - one for the immobiliser and another for the habitation area, as the alarm has gone off before, with no flashing indicators (the same as above example), then when I couldn't disarm it externally, I went in through the habitation door and the alarm became a lot louder and the indicators started flashing. I was then able to disarm the alarm immediately by pressing the alarm fob button.

Really weird

Hello, I am having exactly the same problem with my 1998 SWB 640, no flashing indicators, just a lous audible alarm ( in the middle of the night...twice) looked at all the wiring, battery seems fine, the master key thing is new to me, I have no button on the fob ( too old ) but will try the other key next time, I have to disable by taking the negative terminal off my battery, you would think when I connect the battery up again it would go off immediately but all is well....I am keen to get an Auto electrician, however if he knows nothing about these it will be a wasted excercise, and advice greatly appreciated,

Maybe you're expecting too much from an almost 20 years old circuit.
I had no idea what "Serpi Star" was, so I looked it up. With alarm contacts all over the place it could be very time consuming to locate the problem. It also seems to be triggered by a voltage drop, something not unusual in an old vehicle.
Getting rid of the alarm device may involve a lot of rewiring, but you could open the box and disconnect the siren. Waking up in the middle of the night gets you a bad temper.

The sirens usually have an internal battery so that thieves can't simply cut the wiring to it. When the internal battery starts to fails you can have random triggering