Scientistsu, engineers, and doctors yearn for tiny sensors to record a vast array of events in the world's many hard-to-reach places. And so far, the tradeoff between battery life and size has prevented sensors from becoming small enough to fit unobtrusively in the human body, or inside very small machines. Now, University of Michigan researchers seem to have solved that puzzle by creating a chip that draws energy through solar power, heat, or movement. By forgoing a large battery for perpetual environmental power, the U of M scientists managed to produce a sensor 1,000 times smaller than any other similar device.