The Waterpebble is a small disc that gets placed near the shower drain. When it's first used, it learns how long the user's showers typically are. Then, on subsequent showers, it uses a series of "traffic light" signals ranging from green to red to tell consumers when to finish. Each time it's used, the Waterpebble fractionally reduces the length of the user's shower, resulting in water savings without the need for any conscious effort.
Source: springwise.comAdded: 5 November 2010