Energy harvesting is a technology that gathers energy such as sunlight, artificial light, and vibration and heat from machinery to obtain electric power. Applying this technology to wireless sensor modules in a machine-to-machine (M2M) wireless sensor network will eliminate the need for grid-based power and primary batteries and create new value in the form of maintenance-free, battery-free, and cable-free operation. Energy harvesting can also promote environment-friendly, clean technology that saves energy and reduces CO2 emissions, which makes it a useful technology for achieving the next-generation smart city and sustainable society. This paper introduces oxide-based thermoelectric material, all-solid-state secondary battery technology, and energy-harvesting tester technology now being researched and developed at Fujitsu Laboratories as elemental technologies for applying energy harvesting technology to M2M wireless sensor modules and achieving maintenance-free operation. © 2014 Fujitsu Ltd. All rights reserved.