Thanks for the reply, I can confirm that the alarm is the factory fitted TVSS IIIB. The car starts fine - plenty of juice in the main battery. I have just found out that when the alarm is "tripped", the siren now makes a high pitched, but not very loud, even sound.... not the ear shattering noise it used to make! It does sound b***ered doesn't it? If I take off the siren (the bit under the battery tray) am I liable to have troubles with the immobiliser? I don't want to render the car unusable but being an avionics engineer I may be able to fix a knackered siren. Also - if I disconnect the battery, will the immobiliser activate when I reconnect it? I really don't want to be left with an immobilised car that has to be towed to Mr T. Thanks again for your help, Dave JJ