Method for detecting an end-of-dose condition in a pressurized system, comprising the steps of (a) providing a system having a fluid-filled variable volume reservoir comprising an elastically deformable portion and an outlet, pressurizing means, and means for detecting a property of the elastically deformable portion which varies with the internal pressure in the reservoir, (b) pressurizing the reservoir to expel a desired amount of fluid by applying a force, thereby deforming the elastically deformable portion, (c) measuring, after the actuating step, a property related to the elastically deformable portion as it regains its initial configuration, (d) comparing a value for the measured property with one or more threshold values, and (e) providing a user with an indication when a given threshold value has been reached, and/or when a given threshold value has not been reached within a given period of time.
