An andon is a signal used to alert people to a problem with a process. Andons support jidoka, the component of the Toyota Production System that means automation with a human touch. The goal of jidoka is to improve quality, and an andon is a signal that can identify quality problems right away.
Andons come in several forms. For example, a light post with a green, yellow, and red light that changes color when a problem arises is an andon. Electronic andons can display the state of current processes on a screen, and images or text can change color. Any signal that is triggered by a process issue is some kind of andon.
In daily life, many andons exist outside the workplace, too. When the fuel warning light comes on in a car, that's a signal to refill the vehicle's gas tank so the process of driving can continue. If someone leaves the refrigerator door open in the kitchen, some fridges will start beeping to alert people to take action and close the door.