If this sounds extremely strange, that’s because it is, at least for western culture. Know as the “Sound Princess” when translated into English, this device was first introduced in the 80’s and has since spread to almost every public women's rest room in Japan.
Why exactly is this necessary? Many Japanese women are self-conscious of being heard going to the bathroom by other women so they would flush continuously. This action wasted such copious amounts of water that it became a problem.
Instead, the Water Princess was introduced to save water. When a button on the Sound Princess is touched, a loud artificial flushing noise will be made.
Estimates say that up to 20 liters of water are saved each time the device is used. Even so, many women believe it sounds too artificial and like the good old natural sound of a flushing toilette.