Hi, had the dreaded alarm siren failure by corroded batteries etc. Fitted a new second hand unit today and still hazards flash but no sound. Scanned with vcds lite and get... 01134 alarm horn h12 29.00 short to ground. soon as I clear it then it returns. Im not actually sure it's a fault of if the rechargeable cells inside have to charge up first before I will hear any sound. Does anyone know ? Many thanks.