Be a traveling meteorologist with this anemometer attachment for your smartphone. The Vaavud actually works without using any electronics (other than your iOS or Android phone and an app). Inside the rotor of the water, sand, and dirt-resistant Vaavud are a pair of magnets. The app uses your phone’s built-in magnetic field sensor and an algorithm normally used for sound processing to determine how fast those magnets are moving and then displays the wind speed.

Smartphone Wind Speed Meter (Anemometer)