Medication delivery system with a detector for providing a signal indicative of an amount of a set and/or ejected dose of drug

A medication delivery device (100), comprising:

• A piston rod (154) for advancing a piston (152) for forcing drug out of a drug containing compartment (150) of a housing (151, 160),
• a movable part (156) connected to the piston rod (154) and adapted to rotate relative to the housing (151, 160) to move the piston rod (154) distally with sufficient force to expel the drug from the delivery device;
• at least two conductors comprising a first electrically conducting surface (200) and a second electrically conducting surface (202)which are arranged such that an electrical characteristic is defined by the mutual position of the movable part (156) and the housing (151, 160);
• and
• a detector for detecting a change of said electrical characteristic, wherein the movable part (156) comprising the first electrically conducting surface (200) and the housing (151, 160) comprising the second electrically conducting surface (202) are stationary relative to each other during dose setting and in that the movable part (156) and the housing (151, 160) are rotated relative to each other during dose ejection, such that the detector provides a signal indicative of the actual amount of the ejected dose.