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 and which engages therewith, the annular component being configured to impart a rotational movement about the longitudinal axis to said dose selector shaft ; wherein the substantially annular component comprises means for producing a three-dimensional magnetic field ; and magnetic field detection means 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 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 and which engages therewith, the annular component being configured to impart a rotational movement about the longitudinal axis to said dose selector shaft ; wherein the substantially annular component comprises means for producing a three-dimensional magnetic field ; and magnetic field detection means 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 are located in said first or said second component, or distributed between said first component and said second component . <EOS>