Here is a very cheap looking product designed for complete idiots who don't want to do anything for themselves. Or those who'd like to pretend that they live in a mansion and have servants who run their bath for them.
The idea behind the Shower Light is, as you may have gathered, to "never jump in a cold shower again." Who does that? What are we, cartoons? High-energy sitcom characters? You stick your hand under the water, and if it's too hot, you scream, "Too @#$%ing hot!" and then you adjust it so that it's not.
I really hope this thing malfunctions and burns the shit out of whoever uses it.
Shower Light™ - never jump in a cold shower again! When you first turn on the faucet, blue light shines down through the stream to indicate the water is still cold. When the water reaches a comfortably warm temperature (89°ree; F), the LED light changes to red. No batteries or special tools needed. Quick and easy to install, fits a standard shower pipe. Plastic, 5 x 4 x 4". $49.98