Drug injection device (400) comprising expelling means for expelling an amount of drug from a reservoir, the expelling means comprising setting means (411) allowing a user to set a dose to be expelled, and actuation means (413) for releasing the drug expelling means to expel the set dose. The actuation means comprises an actuation member adapted to be moved between an initial position, an intermediate position, and an actuated position in which the expelling means is actuated to expel the set dose. The device further comprises an electronically controlled capturing system (420) for capturing data representing the amount of drug expelled from the reservoir by the expelling means, and switch means for starting initialization of the capturing system when the actuation member is moved to its intermediate position.