An aerosol delivery system comprising: an aerosol generator comprising a vibrating aperture plate and an actuator (11, 16, 17, 19), wherein the aperture plate has a plurality of apertures extending between a first surface which is adapted to receive a liquid to be aerosolised and a second surface at which an aerosol is generated, and a controller (18, 19) for controlling operation of the aerosol generator, wherein the controller is configured to perform in real time a method comprising the steps of:- monitoring at least one electrical characteristic of the aerosol generator as it is driven for vibration of the aperture plate; detecting a change in the electrical characteristic in response to a transition from a wet state to a dry state of the aperture plate; and automatically modifying (203, 205, 206), during said transition, operation of the aerosol generator in response to said detected change, said modification including reducing power applied to the aerosol generator, characterized in that, the controller is configured to: monitor a signal representing the electrical characteristic at each of a plurality of drive frequencies, maintain data representing a trend in each signal and/or in a combination of the signals, identify a start of a transition if a calculated value representing deviation from said trend or trends rises above a threshold, continue to monitor said change during the transition, including monitoring the aperture plate for presence of residual liquid on the aperture plate first surface, wherein there is more than one threshold level, including a low level to provide an initial indication of potential transition, one or more intermediate level or levels which provide an indication of whether a rise is noise or due to a transition, and a top level which triggers immediate shut-down of the aerosol generator. an aerosol generator comprising a vibrating aperture plate and an actuator (11, 16, 17, 19), wherein the aperture plate has a plurality of apertures extending between a first surface which is adapted to receive a liquid to be aerosolised and a second surface at which an aerosol is generated, and a controller (18, 19) for controlling operation of the aerosol generator, monitoring at least one electrical characteristic of the aerosol generator as it is driven for vibration of the aperture plate; detecting a change in the electrical characteristic in response to a transition from a wet state to a dry state of the aperture plate; and automatically modifying (203, 205, 206), during said transition, operation of the aerosol generator in response to said detected change, said modification including reducing power applied to the aerosol generator, characterized in that, the controller is configured to: monitor a signal representing the electrical characteristic at each of a plurality of drive frequencies, maintain data representing a trend in each signal and/or in a combination of the signals, identify a start of a transition if a calculated value representing deviation from said trend or trends rises above a threshold, continue to monitor said change during the transition, including monitoring the aperture plate for presence of residual liquid on the aperture plate first surface, wherein there is more than one threshold level, including a low level to provide an initial indication of potential transition, one or more intermediate level or levels which provide an indication of whether a rise is noise or due to a transition, and a top level which triggers immediate shut-down of the aerosol generator. monitor a signal representing the electrical characteristic at each of a plurality of drive frequencies, maintain data representing a trend in each signal and/or in a combination of the signals, identify a start of a transition if a calculated value representing deviation from said trend or trends rises above a threshold, continue to monitor said change during the transition, including monitoring the aperture plate for presence of residual liquid on the aperture plate first surface, wherein there is more than one threshold level, including a low level to provide an initial indication of potential transition, one or more intermediate level or levels which provide an indication of whether a rise is noise or due to a transition, and a top level which triggers immediate shut-down of the aerosol generator.