Unidentified Covenant explosives vest
From Halopedia, the Halo wiki
After being captured by Jul 'Mdama's Covenant, Dr. Henry Glassman was outfitted with one of these vests along with a leash to help keep him under control as he worked on "Librarian's Rest" in exchange for his life.
When Glassman inadvertently activated the shrine's security system, he took the opportunity to escape, chased by several Sangheili Storm and Gek 'Lhar who carried the vest's detonator. At the door, Glassman was rescued by Spartan Gabriel Thorne who had himself been captured and escaped. With more Sangheili charging them and Gek arming the vest, Thorne removed it from Glassman and tossed it at the charging Covenant forces. Unaware that the vest had been removed from Glassman, Gek detonated it as punishment for Glassman's escape, killing all of the pursuing Sangheili while Thorne and Glassman escaped. Gek was left both saddened and enraged to find the carnage left behind by the detonation.
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