With the intention of helping you conserve both water and energy, the Smart & Blue Hydrao Loop showerhead is just plain sexy as well.
Install the showerhead, and it will glow different colours to advise how much water you're using. When your shower takes a bit too long, it might turn from blue to pink, then to red to alert you that you might want to step out and dry off.
It won't actually cut off the water supply, so no worries about having your lather session cut short. But it can serve as a nice reminder that you're using too much water - something any household with multiple teenagers know all too well.
The design is such that the showerhead draws its power from the water - no batteries are needed. Keep your existing showerhead by using the Hydrao Drop instead, a dongle that sits between the showerhead and water supply.
Both are set to be available by the end of the year, with pricing TBA.