A medicament delivery device includes a proximal sub-assembly and a distal sub-assembly configured to be connected to each other. The proximal sub-assembly includes a key member, and the distal sub-assembly includes a power pack unit having a lock mechanism for locking the power pack unit such that unintentional activation of the power pack unit during transportation is avoided. The key member is configured to interact with the lock mechanism during assembling of the proximal and distal sub-assemblies such that the lock mechanism is released.
