Researchers at the University of Michigan have created a mini sensor that draws its energy from micro sized solar panels as well as heat and or movement. The sensor is 0.10" by 0.14" by 0.03".
The sensor only needs one nanowatt to operate-that's one billionth of a watt. Most of the time it would be in sleep mode and only waking to record movements or changes. They're thinking possible uses would be inside the human body to monitor head and eye pressure, tumors, environmental changes, building and bridge monitoring.
Read about the tiny solar powered sensor here at Physorg.com.