Neural interface
From Halopedia, the Halo wiki
The Neural Interface is a technology used by the UNSC military. The Standard Neural Interface has basic functions. It acts as a "Friend or Foe" indicator, so that radar signatures will pick up the owner's signature and identify it as friendly. This way, the wearer appears as a "yellow" blip on the motion tracker of other soldier's HUD and friendly fire is less likely.
The Neural Interface is implanted at the base of the skull and cannot be removed without killing its owner. The standard interface is implanted in all UNSC military personnel upon activation, but it can be replaced with a more specialized Neural Lace should the need arise.
Ship Commanders recieve Command Neural Interfaces, while the Spartans have recieved the more specialized Spartan Neural Interfaces.
