sealed prefilled drug reservoir 20 which is formed in the volume between a rigid reservoir wall 22 and a flexible reservoir wall 24 the pump may further comprise an actuator 26 which expands and by doing so moves the flexible wall 24 towards the rigid wall 22 thereby compressing the drug reservoir 20 in order to expel the drug the drug reservoir 20 further comprises a septum 28 at the end of a conduit 29 leading from the drug reservoir 20 said septum 28 sealing said reservoir while allowing penetration thereof using a hollow penetrating member referring now to fig3 a this figure shows how in this preferred embodiment the safety cover 14 comprises an internal pin 30 which serves to restrain a first spring 32 in its compressed state fig3 b then shows how the removal of said safety cover 14 enables said spring 32 to expand until it hits a stop 34 referring now to fig4 a a planar view showing the spring 32 in its compressed state is shown and then fig4 b shows how the release of said spring 32 causes a penetrating member 40 to pierce said septum 28 emerging in said conduit 29 thereby effecting a fluid connection between the interior of the drug reservoir 20 and the fluid passageway 42 leading to the cannula 44 the prefilled drug reservoir 20 is stationary relative to a central longitudinal axis defined by the assembly containing cannula 44 during penetration of the sealed prefilled drug reservoir 20 by the selectively activatable penetrator penetrating member 40 fig5 a shows an enlarged side perspective view of the device the septum 28 and its piercing by the penetrating member 40 are seen in this view fig5 b shows an exploded view of an embodiment of a fluid.