Active RFID, meaning where there is a power source in the tag, wristwatches, talking gift cards and much else have something in common. They employ button batteries which need replacement and add up to quite an inconvenience and expense as well as a disposal problem and their bulk can also be a problem. Eventually, ubiquitous energy harvesting will permit most of these batteries to be replaced by energy harvesting, sometimes involving a smaller battery of longer life and sometimes none. A good illustration of this button battery challenge is the relatively new market for Real Time Locating Systems, a form of active RFID where the tag can signal its position in real time most of the time. We therefore forecast this billion dollar opportunity in more detail in chapter 9. Providing long life and low cost to products like these by means of energy harvesting create substantial markets including about 50 million car key "remotes" (clickers) yearly and one billion wristwatches yearly. The number of batteries that the average person and the average business has to replace regularly is rapidly escalating, leading to intolerable time-wasting, cost and pollution.