The Vaavud mobile wind meter is double dipping back into the Kickstarter pool to raise funds for the gadget's second version. The original plugged into a smartphone's audio input jack and, without using any power, could use sound waves to tell your phone the speed of wind. The second generation Vaavud would do the same thing, but in addition to telling you the wind's speed, it would also be able to determine the direction of the wind. This is possible through an optical sensor and some pretty intense math.
If successfully funded, the mobile wind meter would become the world's first handheld gadget that could measure both wind speed and direction. The prototype design is still being fine tuned as it is currently a bit bulky.