An injection device for injecting automatically a medicament comprises an occlusion detection system with a force measurement unit and two separate occlusion detectors. The occlusion detectors take force measurements at different respective measurement rates and generate occlusion indicating signals based on a set of force measurements taken at the respective measurement rates. The injection device further comprises an alarm generator for generating an occlusion alarm signal in cases where either or both of the occlusion detectors generate an occlusion indicating signal. The two occlusion detectors operating at different measurement rates make it possible to detect occlusions more reliably over a broader range of delivery rates.