According to an embodiment, a behind-the-ear (BTE) hearing aid unit is disclosed. The unit includes a housing comprising a hollow inner section defined by an enclosed wall surface made of a single inseparable unit, an electronic module, and an ear hook that is permanently or detachably attached to the housing. The housing extends completely along a single curved axis running along the enclosed wall surface from a first end of the housing comprising the ear hook and a second end of the housing opposite to the ear hook. The housing comprises an inlet opening at the second end, wherein the inlet opening is adapted to receive the electronic module in the hollow inner section and the electronic module is adapted to move from the inlet opening along the single curved axis.