A device for delivering a medicament into the body of a patient by injection into or through the skin of a patient, comprising: a housing (705, 770) having a bottom surface adapted to contact the skin of a patient, a needle aperture on said bottom surface and a top surface; an injection needle adapted for penetration of tissue and for movement through the needle aperture; a reservoir, disposed within said housing, said reservoir in fluid communication to the injection needle; a pressurization system for pressurizing the reservoir; a shielding member adapted for movement away from the bottom surface, the shielding member having a covering portion disposed about the needle aperture, and at least one stanchion protruding from the covering portion, the shielding member having a first position wherein the stanchion of the shielding member is initially disposed within the housing and the covering portion is substantially co-planar with the bottom surface of the housing, and a second position wherein the sleeve of the shielding member is partially withdrawn from the housing and the covering portion at least partially covers the needle; and a biasing element disposed within the housing adapted to bias the shielding member towards the second position of the shielding member; a movable interposer having a first position, which prevents movement of the shielding member, and a second position, which allows movement of the shielding member; characterized in that when the device is placed upon the skin of the patient and activated, the interposer is moved from a first position to a second position whereby the biasing element is allowed to bias the shielding member into the second position, thereby, as the device is removed from the skin, the shielding member emerges from the housing and at least partially covers the needle, and wherein the interposer is a moveable mouse-trap door. a housing (705, 770) having a bottom surface adapted to contact the skin of a patient, a needle aperture on said bottom surface and a top surface; an injection needle adapted for penetration of tissue and for movement through the needle aperture; a reservoir, disposed within said housing, said reservoir in fluid communication to the injection needle; a pressurization system for pressurizing the reservoir; a shielding member adapted for movement away from the bottom surface, the shielding member having a covering portion disposed about the needle aperture, and at least one stanchion protruding from the covering portion, the shielding member having a first position wherein the stanchion of the shielding member is initially disposed within the housing and the covering portion is substantially co-planar with the bottom surface of the housing, and a second position wherein the sleeve of the shielding member is partially withdrawn from the housing and the covering portion at least partially covers the needle; and a biasing element disposed within the housing adapted to bias the shielding member towards the second position of the shielding member; a movable interposer having a first position, which prevents movement of the shielding member, and a second position, which allows movement of the shielding member; characterized in that when the device is placed upon the skin of the patient and activated, the interposer is moved from a first position to a second position whereby the biasing element is allowed to bias the shielding member into the second position, thereby, as the device is removed from the skin, the shielding member emerges from the housing and at least partially covers the needle, and wherein the interposer is a moveable mouse-trap door.