Thanks for that Good Gourd.
It would be a very good idea for allotment association to buy in bulk too. The amount of sheds, etc etc that I have in mind to use these (plus 5) think I might be looking at bulk buying myself! ;D
Only joking, think I'd try one at a time cos OH not the best with alarms and he might well set them all off at once if I suddenly alarmed everything. :o