Magnetic jewel device two centimeters in size that would be implanted in humanoids to facilitate tracking and identifying those implanted. The devices were used on Manu III and Turkana IV to sound an alarm when the wearer would enter a forbidden area. On Turkana IV, they were also useful in warning of enemy cadre members nearby, and to identify what cadre a person was affiliated with. Microexplosives that would detonate when exposed to air were to prevent removal of the detectors, but Dr. Beverly Crusher was able to remove one from Ishara Yar in 2367 by surrounding the surgical area with an inert gas.