A data collection device comprises: a first portion having one or more features configured for attaching of the first portion to a dosage knob of an 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； a sensor arrangement configured to detect rotation of the first portion relative to the second portion； and a processor arrangement configured to, based on said detected movement, determine a medicament amount expelled by the injection device, wherein the coupling arrangement is configured to provide a non-permanent coupling between the first portion and the dosage knob of the injection device.
