My cats always hear food being moved (daren't move the biscuit tin or they're all there looking at me accusingly as if I've just eaten all their biscuits) but would happily sleep through the smoke alarm going off. Infact when i used to live in my flat we had the big bell alarms in each flat (all the flats were hooked upto one big alarm) so if anyone burnt the toast or sprayed an air freshener in their hallway the fire bell would go off. My oldest cats would happily sleep through this going off without even opening an eye, the kitten (she's now 10) would go off instantly and hide under the bed (she's where you get the term scardy cat from as she used to be frightened of her own shadow).