Abstract: The present invention provides a sensor module adapted to be arranged in a cartridge based drug delivery device between a rotatable piston rod and a cartridge piston for capturing dose data from a dose expelling event, the sensor module (50) extending along a reference axis and comprising: a first module part (51) adapted to engage the cartridge piston and comprising anti-rotation means for establishing a frictional interface to the cartridge to impede rotation of the first module part (51) relative thereto, a second module part (54) adapted to engage the rotatable piston rod, and sensor means (52, 152, 252; 53, 153, 253) adapted to detect an extent of relative rotational motion between the first module part (51) and the second module part (54), wherein the anti-rotation means comprises a plurality of radially outwardly projecting studs (51.1; 351.1; 451.1), each comprising a contact surface (51.8; 351.8; 451.8, 451.9) adapted to establish frictional contact with an interior surface of the cartridge.

Abstract: The present invention provides a cartridge system (30) for a drug delivery device, comprising a drug cartridge (20) comprising a cartridge body (21) extending along a reference axis between a distal outlet end portion and a proximal rim (21.2), and a displaceable piston (22) arranged in the cartridge body (21) an axial distance from the proximal rim (21.2), an outer cavity (29) thus being formed between the displaceable piston (22) and the proximal rim (21.2), and a guide element (60, 90) comprising a main guide body (61, 91), and a rim interface member (62, 92) adapted to abut or engage the proximal rim (21.2) and thereby cover the proximal rim (21.2) at least partially. The main guide body (61, 91) extends between a first main guide body end (61.1) bordering the rim interface member (62, 92) and a second main guide body end (61.2) and defines a passage for a sensor unit.