Abstract: A start of medicament delivery notification mechanism is presented where the notification mechanism is positioned within a housing of a medical device and includes a rear cap secured to a distal end of the housing, where the rear cap has a hollow tubular housing extending proximally from a distal end of the rear cap such that the tubular housing is cantilevered within and rotatably fixed relative to the housing and is parallel with a longitudinal axis of the housing. A rotator rotatably is positioned around the tubular housing such that rotator can rotate relative to the tubular housing from a first position to a second position, where the second position coincides with an initiation of a delivery of a dose of medicament. The rotator further has a contact surface that engages with and subsequently disengages from a corresponding contact surface located on the rear cap or on an inside surface of the housing.