Drug delivery devices and related methods of assembly are disclosed. The drug delivery device may include a housing, a container, a trigger member, and an interlock assembly. The trigger member may be selectively moveable relative to the housing to activate operation of at least one activatable element of the drug delivery device. The interlock assembly may include a lever mounted rotatably relative to the housing, a proximity sensor moveable between a first position extending beyond an exterior surface of the housing and a second position retracted toward the housing, and a rotational biasing member operably connected to the proximity sensor via the lever. When the proximity sensor is in the first position, the interlock assembly may limit movement of the trigger member relative to the housing. The rotational biasing member may be configured to exert a torque biasing the proximity sensor toward the first sensor position.
