Hi, in most cases this symptom is caused by the volumetric sensors... lock it with key in the lock not with fob for test cos this disables the volumetric alarm only and if the alarm will rest this way that's it... they used to suffer from corrosion or just simply fail cos it's a PCB with integrated circuits... also this can happen if it's windy outside and the door seals are not sealing well, or a moth trapped in cos the volumetric alarm is triggered by air movement in the cabin
here's a sample
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2000 Discovery Td5 ES manual
Hawkeye v.6, Nanocom EVO,
VDM UCANDAS, oscilloscope
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ALL MY ADVICES ARE BASED ON MY OWN KNOWLEDGE AND MY WAY OF UNDERSTANDING THE DESCRIPTION AND OPERATION OF SYSTEMS... I'M NOT A LAND ROVER TRAINED SPECIALIST JUST AN ADDICTED ENTHUSIAST.