It has just been announced here in New Zealand, that all new houses and alterations, are required to have Smoke Detectors installed in them.
These are to be mains-operated and are to be run from a dedicated circuit.
This is great as far as Fire Safety is concerned, I know that the NZ Fire Service has been lobbying the NZ government for years to get this law passed.
Are smoke detectors compulsory where you come from?.