This paper presents the design, analysis, and experimental verification of a piezoelectric device that extracts energy from low-level vibrations. Such a device may be configured as a new source of power supply to operate wireless sensor networks. A millimeter-sized, non-uniformly shaped beam consisting of two piezoelectric layers is proposed as the key component of the device. An analytical model of the beam is established and used to predict the dynamic response of the beam and subsequently, its power output, when it is subject to vibration inputs. Through a coupled-field analysis, the coupling between the mechanical and electrical domains of the energy extraction device is analyzed. Simulations and experiments on a vibration shaker have shown that, compared with the rectangular beam design that has been traditionally used, the new design has increased the energy extraction capability of the beam by as much as 70%. In addition to beam design, issues related to device packaging are also addressed in the paper.