One of the major hurdles in wide spread use of wireless sensor networks is power consumption, i.e., the battery limitations. For several years, researchers tried to minimize power consumption of wireless nodes by designing more efficient data collection, transmission, storage, and processing methods. In this position paper, we will review the paradigm changing battery-free wireless sensing, which was originally designed for monitoring NASA's inflatable lunar habitat and ended up being commercialized for monitoring jet engines, brain injury detection, and indoor navigation.Theory and practical applications presented in this paper will cover basic research in a University lab to commercial products for Army, Air Force, NASA, NFL and several future directions.