1. A control apparatus comprising a housing and adapted to control a hearing device in dependence on recognising predefined gestures made by a wearer of the hearing device by moving one of his or her arms and/or the hand of said arm relative to the housing when the housing is in an operating position at or on the wearer's body, the housing comprising a reference electrode arranged to couple capacitively to a body area of the wearer when the housing is in the operating position and a first sensor electrode, the control apparatus further comprising: a first signal generator adapted to provide a first electric probe signal between the first sensor electrode and the reference electrode; a first measurement circuit adapted to determine first signal values in dependence on the impedance between the first sensor electrode and the reference electrode; a detector adapted to recognise said gestures in dependence on the first signal values; and a control unit adapted to provide control commands to the hearing device in dependence on recognised gestures, wherein the first signal generator is adapted to provide the electric probe signal at multiple signal frequencies; the first measurement circuit is adapted to determine the first signal values at multiple signal frequencies; and the detector is adapted to recognise said gestures in dependence on changes in ratios between the first signal values determined at different signal frequencies.