Toad Ai606 alarm fault?

Hi, I have aToad Ai606 alrm fitted but it just activates for no reason day or night rain or shine in the garage or outside. Toad arranged for an engineer to 'service' the alarm, the guy came from gap security spent an hour telling me I had a fault but couldn't diagnose it. The enginneer suggests a new 'BRAIN' is required but can't guarantee it. Toad have said installation of a new £324 system is the answer.
Can I buy a replacement cpu / brain from somewhere?
Thanks
John Hill