Andon

Andon is one of the most copied and most poorly imitated parts of the Toyota Production System. The hardware is easy to install: lights, towers, buttons, boards. The system behind the hardware is harder to build. Andon works only when operators trust that pressing the button gets them help rather than blame, and when team leads respond fast enough to matter. Without those two conditions, an andon installation is decoration.

"The button is cheap. The trust to press it costs years."

How andon works

An andon system has four parts: a trigger, a signal, a response, and a record. The trigger is whatever lets the operator raise the alarm: a pull cord, a push button, a scanner, sometimes a sensor that detects an out-of-spec condition automatically. The signal is the visible and audible alert: a light at the workstation, a corresponding light on a central board so the rest of the shop knows where the issue is, and usually a buzzer or chime so the team lead does not have to be watching the board.

The response is the part most shops underbuild. A signal without a fast response is just noise. In a working andon system, the team lead arrives at the workstation within seconds, listens to the operator describe what happened, and either solves the issue on the spot or escalates to a planned stop at the next natural breakpoint. The operator does not leave the workstation, the lead does not pull the operator away from the work, and the rest of the line continues until the issue is bounded.

The record is the discipline that makes andon worth more than a fire alarm. Every signal gets logged with the timestamp, the workstation, the operator, the issue, and the resolution. Over a few weeks the log surfaces patterns: which workstations signal most often, which issues recur, which root causes have not actually been fixed. The patterns drive the next round of poka-yoke and standard-work updates. Without the record, the andon system catches problems but does not prevent them.

The signaling devices themselves come in many flavors. Stack lights at each station are the most common. Andon boards mounted high on a shop wall give a building-wide view. Some shops use color-coded paddles or flags at workstations for low-tech versions. The hardware does not matter much. What matters is that the signal is unmissable from across the shop floor and that the response is fast.

Where andon fits on the shop floor

Imagine a 25-person packaging shop running three filling lines for a small consumer brand. Before andon, when something went wrong, operators would either stop the line and walk to find the supervisor or keep running and hope the issue resolved itself. Either response cost time. Quality drift went unnoticed until the back end of the line caught defects, by which point a thousand units had already been packed.

An andon rollout would install a three-color stack light at each line and a single shared monitor at the supervisor's desk showing each line's status. The rule is simple: yellow means the operator needs help but the line can keep running for now, red means the line is stopped or about to stop. Within two months, the supervisor's path through the shop is no longer reactive. The signals route attention to where it is needed. Defect rates drop because issues get caught at minute two instead of minute forty.

That is what andon looks like in a small shop. Three colors, a buzzer, a fast response, and a log. Not an enterprise installation.

Common mistakes with andon

• Installing the lights without granting authority. An andon button operators are afraid to use is decoration. Authority precedes hardware.
• Treating signals as failures. A shop that punishes operators for pulling the cord trains them to hide problems. The metric that matters is fewest defects passed downstream, not fewest signals raised.
• Slow response. A signal answered ten minutes late teaches the operator that the system is not worth using. Sub-minute response is the bar.
• No record. Without a log, andon catches problems but does not surface patterns. The log is what turns andon from reactive to preventive.
• Overbuilding the technology. A shop that installs an enterprise andon platform before establishing the response discipline gets a dashboard nobody trusts. Start with stack lights and a logbook.

Andon and related Lean tools

Andon is the most visible mechanism of jidoka, the lean principle of stopping production when something is wrong. The trigger most associated with andon is the andon cord, though buttons and sensors are equally valid. Behind every andon signal is the same investigative discipline that drives poka-yoke: finding the root cause so the next signal at that station is for a different problem, not the same one.