...craig and his mate have just sorted the heat detector out....replaced it, in point of fact...with a new model which has an inbuilt battery and so the battery doesn't need to be replaced....and more than that - apparently it will keep on running...and for 3 months - even if there were a powercut for that amount of time...his mate, was to laugh...and what else can I say but how efficiently and smoothly - the whole operation went...in and out within the space of about 10 minutes...go figure.