A rod of Kel was an ancient weapon of Vulcan design that was made before the Reformation. They were psionic-based technology devised by trained Vulcan telepaths who crafted the silvery rods that had Vulcan writing inscribed on their surface. Each rod drew upon the telepathic energies and lifeforce of the user in order to operate with not only Vulcans but other telepaths being able to use them. This energy could be used to fire powerful psionic short ranged blasts that wounded enemies or could be used for either feats such as healing.
Being of psionic in nature, the weapons damaged enemies on a neural level and disrupted their cellular structure. Furthermore, they completely ignored any form of armor that they target may be wearing. However, as they drew upon the users lifeforce, it meant that there were potential dangers for prolonged use. Continued use of the Rod of Kel as a weapon meant that eventually the user became exhausted and needed sometime to recuperate with them being able to use the psionic device again within half an hour time frame. If they made extended use of the device, the user fell unconscious for a period of five minutes and awoke exhausted due to the strain placed on them.
Though perfectly capable of being used as a weapon, the rod of Kel was capable of being used in the healing arts. It required a wounded person with a single set of injuries to be placed before the user - preferably in a rha-tel trance. Once done, the user began to use their own lifeforce to mend any wounds or injuries in a practice that took sometime to accomplish. After completion, the injured was completely recovered though the intensity of the action meant that the user was incapable of healing another person for the day.
Hundreds or thousands of such devices were crafted by early Vulcan adepts though many were destroyed in the Time of Awakening and during the peaceful message that Surak spoke of namely the embrace of logic. By the 24th century, they became very rare examples of Vulcan psionic technology that were no longer created and it was known that it was difficult to acquire one. (Last Unicorn RPG module: The Way of Kolinahr: The Vulcans)