From Less Batteries to Battery-Less Alert Systems with Wide Power Adaptation down to nWs—Toward a Smarter, Greener World

This survey reviews the state of the art of IoT devices at the low-energy end of the scale: battery-light and battery-less sensor nodes. They are tiny by necessity but expected to be deployed by the billions in the coming years. The article covers battery technology, energy harvesting, energy management, and system activation and response schemes. Furthermore, it proposes battery indifferent architectures and concludes with informative case studies.