A fluid delivery device (1000) comprises:a first subcutaneously insertable element with a distal portion (28) for subcutaneous placement within a human body, the subcutaneous insertable element comprising a cannula (66) with first and second electrodes (120,122) disposed on an inner or outer surface thereofa sensor (2000) that electrochemically interacts with one or more analytes and generates a signal that is representative of a concentration of the one or more analytes, the sensor being disposed on or within the distal portion (28) of the first subcutaneously insertable element andan external device (1001), (1002, 1003) in mechanical contact with a proximal portion (27) of the first subcutaneously insertable element, the external device comprising:a processor (1007) that receives and processes the signal from the sensor (2000) to determine the concentration of the one or more analytes within the human body anda delivery subsystem for delivering a therapeutic fluid via a second subcutaneously insertable element.
