While bluepills have their headjack in use at all times while inside their pods, permanently connected to the Matrix through the power plant, a redpill uses their headjack only during their periodic missions into the Matrix as part of their rebellion against the Machines. Headjacks are located at the base of the skull, just above where the neck meets the back of the head. Approximately 1 inch in diameter, it probably provides room within the otherwise close quarters of the human cranium for a data probe approximately 8 inches in length and 20mm in diameter.