DSS Choker
The DSS Choker is a device installed by Wille around Shinji's neck after his recover from Eva-01. It is designed to explode and kill the wearer, and is intended to be used in the event that the wearer becomes a trigger for an Impact. DSS stands for Deification Shutdown System.
Misato carries the detonator for Shinji's collar. When Shinji escapes from Wille with Eva-09, despite being urged to use it by Ritsuko, Misato hesitates and is unable to kill Shinji after the collar passes out of range.
At Nerv HQ, Kaworu is somehow able to safely remove the device from Shinji's neck and places it on his own instead. During Fourth Impact, Misato eventually detonates the device and Kaworu is killed.
The collar appears to be more than a simple bomb. As Kaworu's device activates, symbols begin lighting up and holographic prisms being circling his neck.
