A second theory suggests that the sai was always a weapon and that it made its way into Ryukyuan history by following the path of Buddhism, migrating from India to China to Okinawan. This theory suggests that the shape of the sai was designed in the image of the human body of the monks who carried them for protection. The rational for this theory is that there is little iron on Okinawa that would be needed to make the sai.
Another more modern theory is that the sai originated with the Okinawan police force who carried them as their personal "side-arm" to control crowds and apprehend criminals. This story gains credibility because one of Okinawa's leading sai practitioners was Kanagushiku (Kinjo) Ufuchiku, a highly regarded police captain who lived from 1841-1926. However, if the sai was a required weapon for the police there should be some evidence in recorded laws or regulations, but there not seem to be written evidence.
Although there is no evidence of weapons being confiscated in Okinawa, there were tight restrictions imposed on their rights to carry their weapons in public. Therefore, Okinawans increasingly relied upon carrying concealed weapons and sai were one of the prevalent weapons used for this purpose. These hidden sai were typically shorter than the modern sai, with straight prongs rather than flared ones so as not to snag on clothing when being drawn. Since throwing the sai was a common technique, the Okinawans routinely carried more than one sai. The sai could be used as a throwing weapon to knock a rider off his horse, not by stabbing, but more by the sheer weight of the sai. Also, a warrior had a spare sai in case he dropped or lost one. A concealed technique to use for in-fighting is a jab with the tip of the sai from the basic grip (blade along the forearm). However, this only is only possible when the sai length extends past the elbow.