When the organist presses the keys of the organ, the sound comes from the air blowing through the pipes. This is because a valve (an opening with a one-way door) opens up to let the air into the pipe, and closes again when the organist stops pressing that key. This can happen in several ways. Traditional organs have what is called a "tracker action". The trackers are thin wooden rods and wires which move backwards and forwards, opening and shutting all the valves. They are worked by levers under the keyboard. A tracker action organ has to have the console right near the organ, usually under the big front pipes.