New alarm/immobiliser advice needed

Having just recently replaced my ageing BMW E34 with a '99 E36 323i Touring, I was amazed to find it wasn't fitted with any alarm or immobiliser as
standard. Any advice as to a decent quality unit/system for DIY fitting? I want to do it myself as I've had to 'undo' for a few friends' motors, the 'work' (Bodges) of several so-called specialists in the past. (I don't specifically need Thatcham approved systems, just reliable and secure) Any info greatly appreciated. Cheers, JB
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