Abstract: For causing a pinprick on a user's skin to obtain a drop of blood, a movable holder which holds a pin, actuated by a spring, is tensioned.In the normal, inactive position of the spring which is shown in the drawing, the pin is on this side of the edge of the end, and there exists a distance X between a radial shaft having a control button and a stop.When the mechanism is triggered, the spring suddenly pushes the holder, and the shaft passes the normal position to reach the stop which limits its course in such a way that the pin projects, attaining a predetermined extreme position and returning automatically to its protected position.