From Halopedia, the Halo wiki
The Threat Sensor, or Threat Detector, is a piece of equipment compatible with the MJOLNIR (GEN3) armor. When deployed, the Threat Sensor emits a periodic pulse in its surrounding area and highlights enemies on the user's heads-up display.
On May 28, 2560, John-117 found Griffin's removed armor in the Tower and took his Threat Sensor for himself. While facing off against Chak 'Lok in order to rescue the imprisoned and tortured Griffin, the Weapon suggested that the Master Chief use his new Threat Sensor to combat the Sangheili's active camouflage. The Master Chief subsequently utilized his new Threat Sensor throughout the rest of the Battle for Zeta Halo.
The Threat Sensor is a usable piece of equipment in Halo Infinite. Players can shoot the device to any surface, including onto enemies themselves. The device then pulses periodically and highlights enemies in red on the HUD. Enemies are highlighted even when they are obscured by solid barriers or cloaked. The Threat Sensor is especially useful in combating Chak 'Lok and Jega 'Rdomnai who make extensive use of their active camouflage in battle.
The Threat Sensor can be upgraded by collecting and spending Spartan cores.
List of appearances