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, a needle aperture and a lower housing comprising an adhesive surface adapted to attach the device to the skin of a patient; 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 with the injection needle; a pressurization system for pressurizing the reservoir; and a shield adapted for rotational movement along an arcuate path substantially perpendicular to the bottom surface; a flat spring in a constant state of exertion towards an unbiased state when the device is positioned against a user's skin and being adapted to deploy the shield to shield the needle, a mouse-trap door adapted to trap the spring by using principles of leverage, the mouse-trap door having a skin contacting portion disposed about the needle aperture and a pivot, the mouse-trap door having a first position wherein the door is folded over the spring, and the door and the spring are substantially co-planar with the bottom surface of the housing, and a second position wherein the mouse-trap door is rotated about the pivot and the shield at least partially covers the needle; wherein when the door is folded over the spring the spring puts pressure at a predetermined spot on the door which is at a predetermined distance from the door pivot, which reduces the force of the spring by a multiplier of the ratio of the distance between the pressure point of the spring and the pivot of the door; wherein when the device is placed upon the skin of the patient, the adhesive surface is temporarily adhered to the skin and when the device is removed from the skin, the force of the spring is sufficient to rotate the door about the pivot from the first position to the second position, as the spring travels to its fully deployed state in which the shield covers the needle. a housing (705, 770) having a bottom surface, a needle aperture and a lower housing comprising an adhesive surface adapted to attach the device to the skin of a patient; 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 with the injection needle; a pressurization system for pressurizing the reservoir; and a shield adapted for rotational movement along an arcuate path substantially perpendicular to the bottom surface; a flat spring in a constant state of exertion towards an unbiased state when the device is positioned against a user's skin and being adapted to deploy the shield to shield the needle, a mouse-trap door adapted to trap the spring by using principles of leverage, the mouse-trap door having a skin contacting portion disposed about the needle aperture and a pivot, the mouse-trap door having a first position wherein the door is folded over the spring, and the door and the spring are substantially co-planar with the bottom surface of the housing, and a second position wherein the mouse-trap door is rotated about the pivot and the shield at least partially covers the needle; wherein when the door is folded over the spring the spring puts pressure at a predetermined spot on the door which is at a predetermined distance from the door pivot, which reduces the force of the spring by a multiplier of the ratio of the distance between the pressure point of the spring and the pivot of the door; wherein when the device is placed upon the skin of the patient, the adhesive surface is temporarily adhered to the skin and when the device is removed from the skin, the force of the spring is sufficient to rotate the door about the pivot from the first position to the second position, as the spring travels to its fully deployed state in which the shield covers the needle.