Human-machine interfaces enable people to control and interact with machines.  For example, keyboards, mice, and touchpads allow users to interact with computers.  Game controllers allow users to interact with game consoles.  Television remote controls allow users to control televisions from a distance.  Voice recognition technology allows users to control machines through voice commands.  Some game consoles have cameras that capture images of the users' body movements to enable the game consoles to determine the users' gestures, and may illuminate the users with infrared pointers to improve the accuracy of determining the gestures.  Some game controllers have accelerometers to determine users' hand movements.  Some devices also have electromyography sensors to measure the electricity activities of users' muscles to determine hand or finger gestures.