Use of a piezo-active device and an appliance and a system including it

A method of operating a piezo-active device including a piezo-electric element and an elastically deformable shell with a substantially closed profile to produce AC output, said piezo-electric element being disposed in said shell, the method comprising the steps of:

• connecting output terminals of said piezo-electric element to input terminals of an electrical circuit adapted to receive an alternating current power-supply;
• and
• supplying power from the piezo-electric element to said electrical circuit by exerting a punctual mechanical action on said device and then allowing it to resonate freely so that, subsequently to said punctual mechanical action, said piezo-electric element produces an alternating current voltage between its output terminals and therefore between the input terminals of said circuit;
• wherein the piezo-electric element is structured to resonate as a mechanical oscillator following the punctual mechanical action.