One can heap endless praises on Korean toilets. But you'd better visit the site www.toilet.co.kr.
We are going to tell you about one innovation in Korean public toilets. Koreans have the greatest respect for all the aspects of visiting a toilet. For instance, for such a delicate topic as emitting sounds.
To cover the confusion both of those in the toilet cabin and of those outside, they have invented a special “etiquette bell”. This is a nice box with a dynamic loudspeaker attached to the cabin wall. It is provided with a large button. You can press this button when necessary and the sound of water flowing from the flush tank is emitted. In half a minute the sound will die away. You may repeat this operation if necessary.

The “copying” principle was used in this case and an ecologically safe solution was obtained: why spending pure fresh water if only one property – sound – is needed. We use sound and save water.