From Halopedia, the Halo wiki
Diane is a detector loaded with every radio frequency and emergency transponder signal known to mankind. It is also capable to recognizing simple energy emissions and decaying batteries. Its effective range is about half a kilometer in every direction and it can fit in a pack on an individual's back. In January of 2557, Rion Forge, captain of the Mariner-class transport ship, Ace of Spades used Diane onboard the wreckage of a CPV-class heavy destroyer, the Radiant Perception, Laconia. Diane located a log buoy left behind by the UNSC Spirit of Fire in 2531 that had been picked up by the destroyer.
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