From Halopedia, the Halo wiki
An auspex array is a long-range scanning system created by the Forerunners. The auspex array can examine slipstream space to look for approaching ships, or probe vast distances in realspace to instantly map local planetary systems. These systems can also detect the subtle changes in planetary or ship atmospheres, which indicates the presence of Flood contamination. Auspex arrays were fitted to Sojourner-class dreadnoughts during the Forerunner-Flood war.
The Covenant would later adopt the auspex array to their own warships. The command center of the SDV-class heavy corvette was equipped with a high-tier auspex array. In addition, highly classified auspex battlenet uplinks were later integrated into the United Nations Space Command's GEN2 versions of RECON-class Mjolnir helmets, featuring state-of-the-art counter-cyberintrusion and firewall routines provided by the Office of Naval Intelligence.
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