The Andon is a visual and audible signaling system used in the Toyota Production System (TPS) to immediately alert management, maintenance, and other workers to a problem or abnormality on the production line.

It is a direct mechanism for implementing the Jidoka (autonomation) principle. Typically, when a machine automatically stops or a worker manually pulls a cord, the Andon panel illuminates—often showing the exact location and type of issue. This immediate, clear communication allows for a rapid response, ensuring that the problem is addressed at the source before any defective parts are passed downstream. The system drives accountability and supports the core goal of "Build Quality In."