A device for delivery of medicament, comprising: - an elongated housing having a proximal end and a distal end; - a container mounted within the housing and having a slidable stopper contained within and configured to contain a liquid medicament; - a non-rotating plunger assembly comprising a plunger rod having a proximal end and a distal end that is in contact with the stopper, an indent and a longitudinal groove, where the plunger assembly is configured to move axially relative to the housing from a ready position and to an end-of-injection position; - a non-rotating protective shield axially slidable with respect to the housing having an outer surface comprising a longitudinal rib terminating in a bearing surface, where the protective shield has a proximally extending beam and is configured to move from a partially extended position, to a retracted position and to a fully extended position; - a rotator configured as a cylindrical tube having an open distal end and a proximal end wall, where the rotator is axially fixed inside the housing and is configured to be rotated by a biasing force from the rib to engage the rib and is configured to rotate further to form an irreversible lock to prevent the protective shield from moving when in the fully extended position; - a coiled spring having a distal end fixed axially relative to the outer housing and a proximal end attached to the plunger assembly such that the coiled spring is in an extended partially uncoiled tensed configuration having accumulated energy when the plunger assembly is in a cocked position; characterised by - a latch independently rotatable in relation to said rotator, which latch is rotatable by the proximally extending beam of said protective shield when said protective shield is moved to said retracted position, from a first position where the latch prevents the plunger assembly from moving axially to a second position where the latch is disengaged from the plunger assembly whereby a protrusion of the latch moves from the indent into the longitudinal groove to allow the plunger to axially move distally relative to the latch, the rotator and the outer housing such that the accumulated energy is transferred to the plunger rod for driving the plunger rod and the stopper a predetermined axial distance within the container whereby the medicament within said container is delivered. - an elongated housing having a proximal end and a distal end; - a container mounted within the housing and having a slidable stopper contained within and configured to contain a liquid medicament; - a non-rotating plunger assembly comprising a plunger rod having a proximal end and a distal end that is in contact with the stopper, an indent and a longitudinal groove, where the plunger assembly is configured to move axially relative to the housing from a ready position and to an end-of-injection position; - a non-rotating protective shield axially slidable with respect to the housing having an outer surface comprising a longitudinal rib terminating in a bearing surface, where the protective shield has a proximally extending beam and is configured to move from a partially extended position, to a retracted position and to a fully extended position; - a rotator configured as a cylindrical tube having an open distal end and a proximal end wall, where the rotator is axially fixed inside the housing and is configured to be rotated by a biasing force from the rib to engage the rib and is configured to rotate further to form an irreversible lock to prevent the protective shield from moving when in the fully extended position; - a coiled spring having a distal end fixed axially relative to the outer housing and a proximal end attached to the plunger assembly such that the coiled spring is in an extended partially uncoiled tensed configuration having accumulated energy when the plunger assembly is in a cocked position; characterised by - a latch independently rotatable in relation to said rotator, which latch is rotatable by the proximally extending beam of said protective shield when said protective shield is moved to said retracted position, from a first position where the latch prevents the plunger assembly from moving axially to a second position where the latch is disengaged from the plunger assembly whereby a protrusion of the latch moves from the indent into the longitudinal groove to allow the plunger to axially move distally relative to the latch, the rotator and the outer housing such that the accumulated energy is transferred to the plunger rod for driving the plunger rod and the stopper a predetermined axial distance within the container whereby the medicament within said container is delivered.