Tykos 30 was an organic tracking device, that could be injected into the blood of a person and would allow the UNSC to track their location over great distances. It has a similar appearance to the yellow liquid blood plasma. After Ruwan Ackerson was injected with Tykos 30, one Marine stated that they could now "track [him] to Mars." The UNSC believed that the Covenant were not aware of its use, and so were unable to track the substance.[1] In reality, the Covenant were able to do so.


  1. Halo: Uprising, Issue #4 ("We can track you. They can't.")