mspohr writes: A few years ago, a Kickstarter was set up to develop a locator tag powered by free radio frequency (RF) energy harvested from the environment. This was called a scam here on Slashdot and was shut down before it was funded on Kickstarter. However, it now appears that the concept is not as far-fetched as some predicted. A UK company CleanSpace has developed a carbon monoxide (CO) sensor which is powered by free RF. A review of the product has been posted on YouTube. It uses Freevolt technology to keep a battery charged and the CO sensor running. Since they have several thousand of these devices collecting data, they do appear to work and it seems to be in the 'not a scam' department.