An on-body medical fluid injection device comprising: a. a housing; b. an injection needle movable between a retracted position within the housing and an injection position extending from the housing; c. an actuator associated with the needle for moving the needle between the retracted position and the injection position, where the actuator includes: i) a button mounted within the housing, said button movable between a raised position corresponding to the retracted position of the needle and a depressed position corresponding to the injection position of the needle; and ii) a spring configured to urge the button into the raised position; d. a resilient bladder within the housing for containing medical fluid for injection through the needle when it is the injection position; e. an end of delivery member within the housing and configured for movement from a first position towards a second position, the end of delivery member including a slot configured to slide over bladder when it is substantially empty of medical fluid so that (i) the bladder prevents movement of the end of delivery member to the second position when the bladder is substantially filled with medical fluid, and (ii) the bladder allows movement of the end of delivery member to the second position when it is substantially empty of medical fluid; and f. a spring tab configured to urge the end of delivery member from the first position towards the second position and wherein the button is configured to (i) engage the spring tab when the end of delivery member is in the first position and the button is in the depressed position and (ii) disengage from the spring tab when the end of delivery member is in the second position so that the button moves into the raised position thereby indicating the end of delivery of the medical fluid injection device. a. a housing; b. an injection needle movable between a retracted position within the housing and an injection position extending from the housing; c. an actuator associated with the needle for moving the needle between the retracted position and the injection position, where the actuator includes: i) a button mounted within the housing, said button movable between a raised position corresponding to the retracted position of the needle and a depressed position corresponding to the injection position of the needle; and ii) a spring configured to urge the button into the raised position; i) a button mounted within the housing, said button movable between a raised position corresponding to the retracted position of the needle and a depressed position corresponding to the injection position of the needle; and ii) a spring configured to urge the button into the raised position; d. a resilient bladder within the housing for containing medical fluid for injection through the needle when it is the injection position; e. an end of delivery member within the housing and configured for movement from a first position towards a second position, the end of delivery member including a slot configured to slide over bladder when it is substantially empty of medical fluid so that (i) the bladder prevents movement of the end of delivery member to the second position when the bladder is substantially filled with medical fluid, and (ii) the bladder allows movement of the end of delivery member to the second position when it is substantially empty of medical fluid; and f. a spring tab configured to urge the end of delivery member from the first position towards the second position and wherein the button is configured to (i) engage the spring tab when the end of delivery member is in the first position and the button is in the depressed position and (ii) disengage from the spring tab when the end of delivery member is in the second position so that the button moves into the raised position thereby indicating the end of delivery of the medical fluid injection device.