Think about it: when you press your finger down key, keyboard temperature will be changed. If we are in trading just after the success of using a heat-sensing camera to snap a photo, you can look through photos to obtain the password.
See chart, you can find 5 is the final press (because 5 the Red). In fact, order password is 12345, you can tell by looking at the color depth.
Metal keyboard has the advantages of metal and high conductivity, temperature changes quickly. Even someone with a heat-sensing camera, it's hard to observe the color order of judgment.