Abstract: In a mount assembly for releasably fastening a housing to a wall, including a wall mount member arranged to be fixed to the wall and a housing mount member fastened to a wall of the housing, the wall mount member is composed of a base fixable to the wall and presenting a tongue and a first elongate detent element so arranged that when the base is fixed to the wall, the tongue is located along the top of the base and extends horizontally and the detent element is oriented vertically and projects away from the wall, and the housing mount member includes a slot in the housing wall and a second elongate detent element so arranged and constructed that when the tongue engages the slot the second detent element can come into positive locking engagement with the first detent element.