A medicament delivery device having a reservoir for holding a medicament, a pressurizing system that dispenses the medicament from the reservoir when operating, a hollow cannula for insertion into a patient, and a fluid delivery path disposed between the pressurizing system and the hollow cannula and communicating the medicament therebetween. The medicament delivery device also has a pressure sensor external to the pressurizing system, sensing a back pressure in the fluid delivery path, and providing an indication when the back pressure drops below a predetermined threshold after the pressurizing system ceases operation.