An apparatus for generating electrical energy from mechanical vibrations of an object is provided. The apparatus comprises a case for housing the object. The case comprises: a first case member comprising a first and a second opposing surfaces, said first case member comprising an internal space between the first and the second opposing surfaces; multiple piezoelectric elements for generating electrical energy from the mechanical vibrations, each piezoelectric element comprises a first and a second end, wherein each piezoelectric element being arranged over the first and the second opposing surfaces at the first end; a second case member movably suspended on the first case member, said second case member interfaces with the second end of piezoelectric elements arranged over the first opposing surface; and a third case member movably suspended on the first case member, said third case member interfaces with the second end of piezoelectric element arranged over the second opposing surface.