The present invention relates to a coupling device for connecting a residual limb liner to a residual limb socket of a limb prosthesis, characterised by: a magnet assembly comprising a permanent magnet sandwiched by a pair of iron bars for creating a magnetic field; a housing comprising a protrusion for intensifying magnetic field and a cavity for receiving the magnet assembly, wherein said housing is embedded at a distal end of the residual limb socket; a controlling means coupled to the housing and the magnet assembly for controlling the magnetic field by rotating the magnet assembly; and a mounting plate coupled to the residual limb liner; wherein the mounting plate is attracted to the protrusion of the housing when the permanent magnet is vertically aligned, thereby attaching the residual limb liner to the residual limb socket; and wherein the mounting plate is repelled from the protrusion of the housing when the permanent magnet is horizontally aligned, thereby detaching the residual limb liner from the residual limb socket.