Good diamond testers identify diamonds based on their electric conductivity instead of heat conductivity. Testers that identify both properties are even more accurate. In addition, a good diamond detector should notify the user if he is touching metal instead of the stone because without this feature the diamond tester is going to indicate that the diamond is real even though it is testing the metal and not the diamond.
Unless a diamond tester is going to stay in the same room all the time, it is a good idea to obtain a model that can work accurately in a wide range of temperatures, as temperature greatly affects the physical properties of stones. If the user is going to use the diamond tester many times during the day, it should have a short warm up time and require a small amount of time to get ready for the next test. It is also better to obtain a diamond tester that has a battery and the ability to operate while plugged into an outlet, as this makes it possible to use the diamond tester for a wide range of purposes and in many work settings. A good diamond tester should also have a retracting tip, as this prevents damage of the tip and lowers the maintenance cost of the device. It is also important to pay attention to the manufacturer of the tester and the warranty that comes with the device.