Helmet recorder

Summary
Helmet recorders are used by almost every Marine in the UNSC. When in combat with the Covenant, they are instructed to turn these recorders on to get as much information on the Covenant as possible. Because such data is scarce, this is an invaluable tactical resource to ONI and the UNSC forces, who often retrieve this data and then debrief the wearer about the data they encountered. They store their information in Recorder Chips.

Apparently, Covenant Ossoonas are equipped with their own versions of Helmet Recorders.