Andon systems rapidly alerts operators about a problem on the assembly line. This urgent alert allows the problem to be addressed on the spot so that the line can return to normal operation. The system typically indicates where the alert was generated, and may also provide a description of the trouble. All work in production line is stopped until a solution has been found. An andon system is one of the principal elements of the lean production approach.

Common reasons for manual activation of the andon are:

• Part shortage
• Defects created or found
• Tools/machines malfunction
• Existence of a safety problem.

The alerts may be logged to a database so that they can be studied as part of a continual improvement process.