The present invention concerns a device for fastening an emitter to a housing comprising a first, manoeuvre element (10) being slidable in a first direction (11, B), a second, activating element (20) being slidable in a second, fastening direction (21) being inclined in relation to said first direction (11, B), whereby the first and second elements (10, 20) are interconnected via at least one cam mechanism (50). Moreover, the device further comprises a third, fastening element (30) being slidable in the second direction (21), whereby the second and third elements (20, 30) are interconnected via at least one fourth, elastic element (40), whereby the third element (30) is adapted to move, in response to displacement of the first element (10) in said first direction (11, B), between a fastening position in which it produces a fastening force onto said emitter (1) and an open position in which the fastening force is released.