Data Collection Apparatus for Attachment to an Injection Device A data collection device comprising a first portion configured for attachment to a rotatable dosage knob of an injection device in which the dosage knob is configured to rotate as medicament is expelled from the injection device, a second portion rotatably coupled with the first portion, wherein at least part of the second portion is movable axially relative to the first portion. The second portion comprises a button which is rotationally fixed relative to the second portion, and moveable between an extended position and a depressed position. The button and second portion are configured such that moving the button to the depressed position causes the second portion to move axially relative to the first portion. A sensor arrangement is configured to detect rotation of the first portion relative to the second portion. A processor arrangement is configured to, based on said detected movement, determine a medicament amount expelled by the injection device. The data collection device comprises a one-way mechanism engageable with the first portion and configurable to permit relative rotational movement between the button and the first portion in a first rotational direction and to prevent relative rotational movement between the button and the first portion in a second rotational direction opposite to the first rotational direction.La présente invention concerne un dispositif de collecte de données, comprenant une première partie conçue pour être fixée à un bouton de dosage rotatif d'un dispositif d'injection dans lequel le bouton de dosage est conçu pour tourner dès que le médicament est expulsé du dispositif d'injection, une seconde partie accouplée rotative à la première partie, au moins une partie de la seconde partie étant mobile axialement par rapport à la première partie. La seconde partie comprend un bouton qui est fixe en rotation par rapport à la seconde partie, et mobile entre une position étendue
