A mounting system for mounting an electric or electronic device in or on a ceiling or a wall, the mounting system comprising: - a back housing adapted for mounting the electric or electronic device in or on the ceiling or the wall; - a front housing adapted to be connected to the back housing by sliding into the back housing; and - a sealing arrangement comprising: - a first sealing member between the front housing and the back housing adapted to provide a seal between the back housing and the front housing, - a second sealing member for providing a seal between the back housing and the wall or ceiling and located around the periphery of a rear portion of the back housing, wherein the rear portion is adapted to be fixed to the ceiling or the wall, - a plurality of third sealing members (24, 25, 26) adapted to cover a plurality of holes (6, 27, 28) defined in the back housing, and - a sealing flap formed by an area in the back housing that is made out of sealing material characterised in that the sealing flap comprises a fourth sealing member located around the periphery of the sealing flap for enhancing the sealing capacity of the sealing flap by touching the ceiling or wall when the mounting system is fixed to the sealing or wall, and in that the first sealing member, the second sealing member, each of the plurality of third sealing members (24, 25, 26), and the fourth sealing member are together formed in one piece to form a master sealing member. - a back housing adapted for mounting the electric or electronic device in or on the ceiling or the wall; - a front housing adapted to be connected to the back housing by sliding into the back housing; and - a sealing arrangement comprising: - a first sealing member between the front housing and the back housing adapted to provide a seal between the back housing and the front housing, - a second sealing member for providing a seal between the back housing and the wall or ceiling and located around the periphery of a rear portion of the back housing, wherein the rear portion is adapted to be fixed to the ceiling or the wall, - a plurality of third sealing members (24, 25, 26) adapted to cover a plurality of holes (6, 27, 28) defined in the back housing, and - a sealing flap formed by an area in the back housing that is made out of sealing material characterised in that the sealing flap comprises a fourth sealing member located around the periphery of the sealing flap for enhancing the sealing capacity of the sealing flap by touching the ceiling or wall when the mounting system is fixed to the sealing or wall, and in that the first sealing member, the second sealing member, each of the plurality of third sealing members (24, 25, 26), and the fourth sealing member are together formed in one piece to form a master sealing member. - a first sealing member between the front housing and the back housing adapted to provide a seal between the back housing and the front housing, - a second sealing member for providing a seal between the back housing and the wall or ceiling and located around the periphery of a rear portion of the back housing, wherein the rear portion is adapted to be fixed to the ceiling or the wall, - a plurality of third sealing members (24, 25, 26) adapted to cover a plurality of holes (6, 27, 28) defined in the back housing, and - a sealing flap formed by an area in the back housing that is made out of sealing material characterised in that the sealing flap comprises a fourth sealing member located around the periphery of the sealing flap for enhancing the sealing capacity of the sealing flap by touching the ceiling or wall when the mounting system is fixed to the sealing or wall, and in that the first sealing member, the second sealing member, each of the plurality of third sealing members (24, 25, 26), and the fourth sealing member are together formed in one piece to form a master sealing member.