Disco alarm problem

Disco Mk 2. Alarm system.
I can lock and arm successfully by turning key in driver side lock but if I arm the system by pressing the fob button the alarm goes off within half a minute.
I assume its something to do with the air movement sensor system as that's the only thing not armed by using the key alone.
Anybody point me in the right direction?

Oh and if its any help, the drivers side door doesn't unlock when you de-activate the system using the fob. It has to be seperately unlocked with the key. All the others open properly.
That pre-dates the current problem and is due to be sorted when it goes in for service/MOT later this month.
Bryan H

We had the same problem with our Disco 1 and I can't quite remember how it was fixed now :doh:

However, I recently took the headlining out in order to repair the leaky sunroofs, and I found that the motion sensor was not connected.

If you're talking about the same thing its the box which is attached to the headlining and has 2 black circly things on each side. It's only clipped on and if you pull it it comes straight off. Have a check of the connector on the back (in other words, wiggle it about!) or, if it isn't connected, reconnect it. Then push the sensor back in and see what happens.

I have no idea about car alarms and how they sense that they're being broken into so, apart from that, I can't give you any more advice.

Hope this helps anyroad

I had exactly the same problem - changed the battery in the FOB. Sorted the alarm but door still a problem.

You a right in that you isolate the ultrasonic movement detector buy locking with a key, so unclip the sensor and disconnect the wiring and leave disconnect and see if the problem goes away if it does then the sensor is faulty.
Door locks do go faulty and they can't be repaired on a D2, but it maybe just sticking so try a splash of WD40 before you go and replace the lock.