Andon is a visual management tool that surfaces abnormal conditions the moment they occur. An operator pulls a cord or presses a button to trigger a light, sound, or board, calling for help and — in a true jidoka system — stopping the line so a defect is never passed downstream.
Andon embodies the principle of "stop the line to fix problems": short-term output is sacrificed to protect quality and to force problems into the open where they get permanently solved.