This article examines how harvesting environmental energy in sensor networks changes the way an application developer views energy management, and discusses prototype devices. Then it proposes devices that combine energy harvesting and data acquisition. Then it explores novel approaches for optimizing the power extracted using piezoelectric materials. The final one explores kinetic and thermal energy harvesting from human users' activities. We usually use energy harvesting systems to convert and collect the environment's energy flows. A new wearable computing concept is considering these energy flows to be data flows as well. Current piezoelectric energy harvesting research falls into two key areas: developing optimal energy harvesting structures and highly efficient electrical circuits to store the generated charge or present it to the load circuit. Our research focuses primarily on the first area, in which the goal is to create small, lightweight structures that couple very well to mechanical excitation and converts the most usable electrical energy.