Engadget just had a post about this little water thermometer for your shower to let you know when the water is hot.
See, what I've always used was this free thermometer I've had since birth, my hand. On some occassion I end up using my eyes too, see when there is water visible in two states, liquid and gas (visible vapor) I know the water is pretty stinkin' hot. Now personally, I enjoy the very hot shower, to the point of looking like I've been somewhat cooked upon exiting the tub.
I do give credit though, in their original post they also suggested you just "feel" it to make sure, but the concern was for parents with small children. I can understand the concern there, I have two small children myself, however my challenge is for them to take even a lukewarm bath, much less hot!
I also believe in the natural consequences of decisions being a great teaching motivator. I can't really explain to you how it will hurt by turning on the water really hot and just jumping in, so let me know when you figure it out for yourself and we'll review.
There was another feature that I thought was kind of neat, a built in clock to let you know how long you've been in there. The more I think of it though, I'm not too keen on that feature either. See for me, the bathroom is like a little vacation from the real world as soon as I step into the glass shower door. No clocks or other stuff like that. Guess it's kind of like casinos, which gives me a little more insight into the game!