SMOKE SIGNAL

A 'smoke signal' is a form of optical communication used over a long distance, developed both in the Americas and in China. By covering a fire with a blanket and quickly removing it, a puff of smoke can be generated. With some training, the sizes, shapes, and timing of these puffs can be controlled. Puffs may be observed from long distance, apparent to anyone within its visual range. With this in mind, signaling stations were often created to maximize the viewable distance. Stone bowls used by Native Americans and the towers of the Great Wall of China are examples of signaling stations.
There is no standardized code for smoke signals; the signals are often of a predetermined pattern discerned by sender and receiver. Because of this, smoke signals tend to only convey simple messages, and are a limited form of communication.