A hair trimming device is detachably mounted on a handle housing a battery for supplying electric current to a motor located in a drive unit of the trimming device. A trimmer unit includes a plurality of trimmer blade assemblies with different configurations and is rotatable on the drive unit for moving a selected one of the blade assemblies to the operative position in which it is coupled to be driven by the drive unit whilst the other blade assembly which is not in the operative position is uncoupled from the drive output of the drive unit.