To read the heat signature on a keypad, you can either walk up to the keypad and look at it with the heat goggles on, use sniper mode at a distance with the heat goggles on, or activate the keypad and turn on your heat goggles there. The order of the buttons will be as follows, based on color: Deep Blue, Blue, Light Blue, Green, Light Green, Yellow, Orange, Red. For example, if you had a Deep Blue button at 1, a Light Green button at 3, a Light Blue button at 4, and a Orange-Ish Red button at 6, the code would be 1-4-3-6. This trick where you use your thermal goggles to read the code punched in by a guard is extremely useful, but only available in the second Chinese Embassy mission as the current temperature in the Embassy is low enough for you to notice a difference on the buttons that were pressed by the guard. The buttons go from a deep red color to a deep blue color. Look for the button that is slightly different from most of the other buttons. Then, look for a lighter blue button and so on. following green, yellow, orange and finally red.