This cool little gadget will monitor your water usage in the shower, to help you try to conserve. Furthermore, it uses the water itself as its power source.
The device does not contain batteries, it harvests the energy for its operation from the running water. The water flow spins a small turbine inside the device. As soon as water runs through the device, it switches on and a small capacitor is charged. The capacitor can supply the display with energy for a few minutes also after the end of the shower. As soon as that energy has been consumed (or at latest after three minutes), the device switches off.
A great example of sustainable technology that can help make a real difference.