I think what Biggeeeee is trying say is that you're highly unlikely to get anyone to tell you how to disable the intruder alarm on a Disco2.
Reason number one is that we don't know you, not wishing to place too fine a point on it, the Disco2 you're asking about might not be the one you own. I've been here for a number of years now and I don't think I would get a different answer to that question.
The second reason is that the intruder alarm isn't a stand alone unit, but an integeral part of the ecu called the Body Control Unit or BCU, and you really don't want to start digging around in that particular nest of vipers.
As the security system is part of the BCU, the system can be disabled or as there are a few function options available these can be altered to suit your needs maybe.
Random alarm activity in most cases is due to the volumetric alarm so as said locking with key is a way to put the volumetric alarm to rest while the other part is working or it can be disabled with tester ...so can be disabled the alarm completely if that's the owner's choice.