Medicament delivery device comprising a housing, which housing is arranged to accommodate a medicament container, - a drive unit operably arranged to act on the medicament container upon activation, - a mechanical activation mechanism operably arranged to be operated by a user for activating said drive unit, - a mechanical activation preventing mechanism in the form of a blocking element (82, 82) comprising a body (84, 130 I, 130 II) that is semi-circular having a central passage that fits around a tubular second section of an actuator such that it may be turned around the second section, and is operably arranged to prevent said mechanical activation mechanism to be activated, - an identification module arranged to be operated by a user, which identification module is designed as an attachable unit to the medicament delivery device, - mechanical keying elements (104; 52, 54) arranged on said medicament delivery device and on said identification module designed to interact with each other when attaching said identification module, such that the activation preventing mechanism is movable to a non-blocking position, by turning the identification module around a longitudinal axis, to allow operation of the activation mechanism; or - first electrical keying elements (112, 114, 158) comprised in said identification module, - second electrical keying elements (110, 118, 120) comprised in the medicament delivery device, containing identification information, wherein said first electrical keying elements are capable of obtaining identification information from said second electrical keying elements, such that the identification information obtained is compared to stored data and authenticated by the identification module, and wherein the authentication causes a deactivation by the identification module of the activation preventing mechanism being moved to a non-blocking position, by turning the identification module around the longitudinal axis, to allow operation of the activation mechanism. - a drive unit operably arranged to act on the medicament container upon activation, - a mechanical activation mechanism operably arranged to be operated by a user for activating said drive unit, - a mechanical activation preventing mechanism in the form of a blocking element (82, 82) comprising a body (84, 130 I, 130 II) that is semi-circular having a central passage that fits around a tubular second section of an actuator such that it may be turned around the second section, and is operably arranged to prevent said mechanical activation mechanism to be activated, - an identification module arranged to be operated by a user, which identification module is designed as an attachable unit to the medicament delivery device, - mechanical keying elements (104; 52, 54) arranged on said medicament delivery device and on said identification module designed to interact with each other when attaching said identification module, such that the activation preventing mechanism is movable to a non-blocking position, by turning the identification module around a longitudinal axis, to allow operation of the activation mechanism; - first electrical keying elements (112, 114, 158) comprised in said identification module, - second electrical keying elements (110, 118, 120) comprised in the medicament delivery device, containing identification information, wherein said first electrical keying elements are capable of obtaining identification information from said second electrical keying elements, such that the identification information obtained is compared to stored data and authenticated by the identification module, and wherein the authentication causes a deactivation by the identification module of the activation preventing mechanism being moved to a non-blocking position, by turning the identification module around the longitudinal axis, to allow operation of the activation mechanism.