What is the Andon cord?
The andon system (行灯) was developed as part of the Toyota Production System. Originally a cord to be pulled (and more recently a button) it allows anyone on the production line to completely stop the line if a defect is found.
A shallow analysis might say this is inefficient as the whole line stops for what could be a minor issue. This is where the true value lies however.
Any defects in production will continue unless they are dealt with. By empowering their workers with complete control they found and removed issues quickly - rather than letting them propagate further down the line where it would be harder to fix them. Another benefit of stopping the line is to stop manufacturing the defective part.
The number and types of error are also logged to further refine and improve the system. This system is part of the kaizen (改善) philosophy of continuous improvement.