According to ads on telly, smoke alarm batteries should be changed annually. We've got three wired-in alarms installed as part of a loft conversion a year ago and I think I've changed the batteries on each of them 2 or three times. Is this usual?
Also, one of them recently started going off for no reason that I could tell. Are they particularly susceptible to dust? It is fairly dusty in that part of the house as there's still a lot of bare plaster around.