Disclosed is a drug infusion system comprising a drug infusion device having a reservoir, a window for viewing the contents of the reservoir, a cannula arranged to be deployed beneath the skin of a patient, and an actuator configured to be manually actuated to drive a medicament from the reservoir to the cannula. The system also has a cannula cover and a needle handle that holds a needle for insertion into the patient. The cannula cover and needle handle are detachably attached to the drug infusion device, and each is attachable to the other. The device further comprises a septum and a septum pincher to seal the device. The device also comprises a pumping mechanism, part of which are a last-dose lock-out mechanism and an occlusion detection mechanism, both of which operate on the same actuator.