Planning permission is not normally required for installing a smoke alarm, though if you live in a listed building or conservation area you should check with your local planning authority.
If you are building a loft conversion, extension or altering the layout of your home building regulations (Part B Fire Safety) would normally apply.
Building regulations require the installation of automatic smoke detectors to all new dwellings and loft conversions.
Advice should be taken on the type of smoke alarm(s) to be fitted, positioning and installation.