An injection device is disclosed which comprise a housing 10, a plunger 40 for expressing a medicament from a syringe 20 and an actuation mechanism 30. The actuation mechanism 30 is arranged in use to move the plunger 40 between a firstrearward position and a second forward position to express a dose from the syringe 20. The injector device further comprises an injection activation sensor 50, arranged to provide an end of dose indication. The sensor 50 comprises an elongate flexible member. The flexible member has a first end connected to the plunger 40 or actuation mechanism 30 such that actuation motion of the injection device acts to move the elongate flexible member 50 relative to the housing. Movement of the elongate member 50 triggers a response to the injection such as an audible and/or tactile injection complete indication.
