Smoke signals

Smoke signals is an early form of the optical telegraph, developed by the native North Americans and Chinese (as in the towers of the Great Wall.) By covering an open fire with a blanket, and suddenly removing it for a short time, a puff of smoke is generated. With some training, the sizes, shapes of, and intervals between these puffs can be controlled in a way that can be observed from a long distance, and used to carry information.

Apparent to anyone within its visual range, the smoke signal is not a standardized code that can be easily translated. Like other forms of communication, the signals are often of a predetermined pattern discerned by sender and receiver. Still, the smoke signal can abide by other universal patterns of communication. For example, as in other distress calls, a pattern of three would indicate a call for help.