I had two 10yr ones fitted by the local fire service just before xmas & i already had 1 battery one installed that was fine, so we have 3 smoke detectors here, had a hazard check & had a panic cos of all xmas lights but releived to know that my plug extentions were safe & good ones
, also they had a a word to my brats about fire safety & what to do in a house fire while they was here too.
So very much covered here