Intuition can notify an application when the user moves the mouse, makes a
menu choice, selects an application gadget or changes the window's size.
To find out about user activity from Intuition, there are two methods:

  * Use the Intuition Direct Communications Message Port (IDCMP) system.
    Input events are received as standard Exec messages at a port
    Intuition creates for your window.

  * Use the console.device to receive all input events as character
    sequences.

 The IDCMP             The IDCMP And The Active Window 
 The Console Device    The IDCMP And Gadgets