There are several possible theories regarding the origin of nunchaku. One is that it may have derived from an instrument used for crushing beans. A second theory is that it was adapted from the instrument carried by the village night watch, which is made of two blocks of wood joined by cord. The night watch would hit the blocks of wood together to attract people's attention and then warn them about fires and protect their property. It is probable that heavy-duty weapons were made and hung with other similar farming instruments, so that they were not detected. The nunchaku may or may not have been joined by a chain, but it is unlikely as the Ryukyu Islands had no source of iron ore and most metals were imported. Cord was the most likely way in which they were secured together.
Unlike the exotic flailing actions portrayed in martial arts movies, the exponent of nunchaku was very conservative in his movements. No true exponent would spin the nunchaku under his legs or around his neck while his enemy was attempting to kill him. The skill was in effective blocks and instant, accurate strikes at the enemy. If the flail hit a target then it would bounce back and had to be brought within the user's control quickly. Like okinawate, nunchaku power was developed through the repetition of kata which developed a powerful and accurate strike. The techniques complemented the empty-hand styles.
-Michael Finn, Martial Arts: A Complete Illustrated History, The Overlook Press, 1988