An arrangement that converts mechanical energy into electrical energy employs a base member and a cantilever member coupled thereto. The cantilever member has two piezoelectric layers with an air space therebetween. A proof mass is coupled to the cantilever member distal from the base member. The first and second piezoelectric layers are formed of lead zirconate titanate (PZT), and the output voltage of the cantilever member is proportional to the height of the air gap. A piezoresistive accelerometer that is useful for measuring mechanical vibration has a suspension beam and a piezoresistive layer be separated from the suspension beam. A method of monitoring an acoustic vibration utilizes a piezoresistive element having an air-spaced cantilever formed of a piezoelectric material in the vicinity of the system to be monitored and obtains an alternating voltage form the air-spaced cantilever of the piezoresistive element.