Instrument of obedience

The instrument of obedience was a circular device implanted subdermally in the temple of each of the inhabitants of the asteroid Yonada. Anyone who strayed from the strict religious doctrines of Yonada could experience pain inflicted through the instrument; repeated offenses could cause death in the individual. (TOS: "For the World is Hollow and I Have Touched the Sky")

McCoy is stricken by the instrument of obedience.

For millenia, in order to become one of the people of Yonada, one had to submit to the insertion of the Instrument. As the Oracle of the People indicated, it was intended to prevent the Yonadans from committing sacrilige or offending against the people or the creators.

This device apparently monitored an individual in an undetermined manner for offensive behavior and thoughts. Examples of such behavior included questioning the Oracle, reading the sacred Book of the People, or even climbing the mountains. At the onset of any forbidden behavior or thought, the instrument would begin to glow and cause momentary pain. If one persisted, the pain increased and death resulted in a matter of minutes.

It was learned by the landing party from the USS Enterprise that the asteroid was constructed by the Fabrini as a multi-generational colony vessel in order to save a remnant of their people from an impending supernova. The survivors were to be guided by a powerful computer, but this computer developed a flaw that led to it setting itself up as the "Oracle", as well as the creation of a repressive theocracy. The use of the instrument of obedience by the Oracle choked off the Yonadan's freedom of thought and expression and ensured that the people would never know that they were actually passengers bound for a new home.

Doctor Leonard McCoy had married the leader of the Yonadans, Natira, and he was bound to accept the instrument. By reading the Book of the People, McCoy learned the secret truth of Yonada – and nearly died as a result. Fortunately, Commander Spock and Captain James T. Kirk were able to remove the instrument from McCoy and Natira before any permanent damage resulted.

Once the true nature of the Oracle was discovered and this knowledge was accepted by Natira, the instruments were removed from the remaining inhabitants and the flaw in the computer was corrected.

See also: neural servo