PAL keys

The PAL key system is a technology used in Metal Gear Solid. They are given to you when you meet Kenneth Baker but do not really become useful until the end of the game. You are told that the PAL key is actually three keys in one: it is made of "shape memory alloy" a technology that allows the way the key is read to change based on the kind of temperature it is exposed to, whether it be low, medium or high temperature.