In my house, we're pretty good about getting in and out of the shower in a reasonable amount of time. All of us except my daughter. If you have a kid that zones out in the shower, this product seems like a pretty good way to help keep them on track.
The Waterpebble sits next to the drain and uses a series of lights to alert the user when to start rapping it up. The yellow light means you should be half way done, and the red light means turn off the water. It even shaves a bit of time off each shower to help train the user to get going faster with each use. It got 4.1 out of 5 by 18 reviewers at Uncommon Goods, so hopefully that means it's more effective than my current method of banging on the bathroom door and yelling.
Waterpebble, available at Uncommon Goods, $10

Nomade Express Slee...
Good teaching device.
I wouldn't lay this on my three-year-old though. Water time is so her thing!
Does it have different settings? Not to stereotype, but generally a girl needs more time in the shower (generally boys have no hair to speak of to wash, and girls have a ton).
The green light says, "Well done - you are saving the planet" . Seriously? Just another plastic gadget that will end up in the landfill & lighten your pocket to boot. Has common sense gone the way of the dinosaur?
I am sure I would enjoy hearing your daughter rap in the shower. I'm old school; I would be especially pleased to hear her rendition of anything by Eminem. If you mean, though, that the pebble warns your daughter to finish up, you meant to write "to start wrapping it up."