Dose control device adapted to be removably mounted onto an exterior peripheral surface of an injectable drug delivery device, the drug delivery device comprising: a substantially elongate drug delivery body, at least one injectable drug held by the body, the body having a distal and proximal extremity, the drug delivery body having a longitudinal axis; a dose selector shaft, aligned substantially coaxially with the longitudinal axis of the elongate drug delivery body; wherein the dose control device comprises: a first component configured to fit and substantially encase at least a portion of an exterior peripheral surface of the elongate drug delivery body, and located at a proximal extremity of said elongate drug delivery body; a second component configured to fit and substantially encase a corresponding remaining unencased portion of the exterior peripheral surface of said drug delivery body, and also located at a proximal extremity of said elongate drug delivery body; wherein said first component and said second component removably engage with each other to form a unit having a longitudinal bore that extends along the longitudinal axis of the elongate drug delivery body, and in which bore the drug delivery body is encased between said first component and said second component; and a substantially annular component mounted on the proximal extremity of the dose selector shaft (27, 28) and which engages therewith, the annular component being configured to impart a rotational movement about the longitudinal axis to said dose selector shaft (27, 28); wherein the substantially annular component comprises means for producing a three-dimensional magnetic field; and magnetic field detection means (8, 34, 35) configured to detect changes in at least the magnetic field produced by the three-dimensional magnetic field producing means; wherein said magnetic field detection means (8, 34, 35) are located in said first or said second component, or distributed between said first component and said second component. a substantially elongate drug delivery body, at least one injectable drug held by the body, the body having a distal and proximal extremity, the drug delivery body having a longitudinal axis; a dose selector shaft, aligned substantially coaxially with the longitudinal axis of the elongate drug delivery body; a first component configured to fit and substantially encase at least a portion of an exterior peripheral surface of the elongate drug delivery body, and located at a proximal extremity of said elongate drug delivery body; a second component configured to fit and substantially encase a corresponding remaining unencased portion of the exterior peripheral surface of said drug delivery body, and also located at a proximal extremity of said elongate drug delivery body; wherein said first component and said second component removably engage with each other to form a unit having a longitudinal bore that extends along the longitudinal axis of the elongate drug delivery body, and in which bore the drug delivery body is encased between said first component and said second component; and a substantially annular component mounted on the proximal extremity of the dose selector shaft (27, 28) and which engages therewith, the annular component being configured to impart a rotational movement about the longitudinal axis to said dose selector shaft (27, 28); wherein the substantially annular component comprises means for producing a three-dimensional magnetic field; and magnetic field detection means (8, 34, 35) configured to detect changes in at least the magnetic field produced by the three-dimensional magnetic field producing means; wherein said magnetic field detection means (8, 34, 35) are located in said first or said second component, or distributed between said first component and said second component.