Interface Headset
An interface headset is an device that's integral to the pilot making a neural connection to the Evangelion. The interface headset is worn on the head by the pilot.
During the course of the show pilots have been set into the Eva without a plug suit, but an interface headset has in most cases been worn by the pilot implying that's it's a necessary piece of equipment, the simulation body tests in Episode 13 and Shinji during End of Evangelion being two exceptions (see Notes).
It doesn't seem to matter what part of the head the interface headset is worn over. Rei and Shinji's are worn near the front of their head, but Asuka apparently wears the interface headset backwards, so that the two small pods are towards the back of her head.
The interface headset is composed of a thin, hairband-shaped wire linking two small pods, possibly containing some form of electronics within which each have a zig-zag design on them similar to the design on their plug suits that goes over their shoulders, they also have two small indentations at the tip. The wire section is nestled beneath the pilot's hair and thus always obscured from view, making it appear as if the headset is comprised of two separate devices placed on top of the head.
Notes
- Exactly what Interface Headsets are and how they function is never explicitly elaborated upon on-screen.
- Asuka Langley Soryu near-constantly wears her Interface Headset, at home and while at school, because she is proud of her status as an Eva pilot.
- Shinji Ikari doesn't wear an interface headset in End of Evangelion, but it would probably have been useless since the Eva was in control, with Shinji effectively as a passenger in the entry plug.