If you want to know whether your coffee in the cup is still hot, you don’t need to test, just get a coffee cup that can tell you.
This clever coffee cup is black and reads “OFF” when the liquid inside it is cold but when the liquid inside is hot, it turns white and reads “ON”.
How about if your coffee is warm, just between hot and cold? I am wondering what colour it will show. Maybe they can invent a latest version cup that the heat sensitive pigment can sense the temperature and change the colour of cup to grey if it the liquid inside is warm.
Anyway, if you think this invention is good enough, you can get one from “Charles and Marie”, it is selling at $25.