It had to come sometime - the process of switching taps (faucets in the USA) on and of using a light-dependant resistor has been around for a long time. Somehow, the concept was not extended to other products until now - Inhabitat talks about a Shower with an electronic cut-off at: http://www.inhabitat.com/2009/03/30/teenage-daughters-taking-too-long-in-the-shower-try-the-aqualim/ Designed by an Australian company, the technology that goes into this product is very simple and home brewers could actually make one of these at home if they wanted to. Hopefully, the concept will catch up in other parts of the world.
In the meantime, the Aqualim company has a stylish and very useful product for anyone who can't be bothered to build one him / herself and who wants to buy a readymade product with the warranties etc that this entails. Check out their website at: http://www.aqualim.com.au/Aqualim_Home.html