An inhaler or add-on device for an inhaler for dispensing a medicament to be inhaled. The inhaler or add-on device has a housing (H) with an air inlet (A_I), and an air outlet (A_O) for outputting air to be inhaled by a user. The housing (H) defines a flow path (FP) between the air inlet (A_I) and air outlet (A_O), and a passive acoustic element (PAE) is arranged in this flow path (FP) inside the housing (H). The passive acoustic element (PAE) has a structure having one or more structured gaps arranged to be passed by an air flow and it is dimensioned such that air flow passing it will generate sound (S) with pre-determined characteristics depending on the air flow speed. This allows acoustic monitoring of air flow passing the first passive acoustic element (PAE) external to the housing (H) by capturing and processing sound generated.