Soon enough, say some engineers, miniature wireless sensors will be located in spots where it would be inconvenient, to say the least, to change their batteries – inside your body, within the steel and concrete of buildings, in the dangerous innards of chemical plants. But today, even the most robust nodes can be counted on to last only a few years. Ideally, engineers need wireless sensors that can last forever without external power sources or battery changes. According to research presented in December at the International Electron Devices Meeting, in Baltimore, that dream is within reach.

What inconvenience is mentioned in the text?