Being awake for less than an [in-game] hour, none of us can say anything for certain. But my theory is that we're inside of a virtual reality, and this? This might be what connects our physical selves to our virtual selves. It's also helpful for the in-game activities--a list of fellow player characters, potentially a future inventory list, a map, rules of the game, so you wouldn't want a player to have any chance of losing, misplacing, or...tampering with the device.