Just having a silly thermometer in the bathtub to make sure either you or your children don't get scalded isn't nearly cool enough. No, you need a silicon disk and a thermometer color guide instead. That way seems much better for gadget lovers.
Alright, I have no idea why it's better, but the silicon disk is waterproof, that's exciting. It does show both Celsius and Fahrenheit, so it'll work both in the US and everywhere else.
Just put the disk in the water and it changes color. At which point you can reference the guide to see how hot the water is exactly. This is still a concept design by Kai Chen and from the looks of it I'd imagine it will stay a concept design.