A tool that allows you to instantly know if a gemstone is a Diamond, and separate it from Diamond Simulants like Moissanite and Cubic Zirconia. You just touch the tip of the tester to the top/Table of the diamond, being careful not to touch the metal Prongs.
But be careful, it is no longer enough to use a diamond tester. You will also need to test for Moissanite because it has similar properties of heat conductivity, which is the most common testing mechanism used in diamond testers. Cubic zirconia has a different heat conductivity than diamond, so the traditional diamond tester is enough. Moissanite has a different electrical conductivity, so you will need to test for that property to separate it from diamond.