The SmartCap Processor card (SP Card) contains all of the critical electronics to calculate fatigue using the SmartCap Universal Fatigue Algorithm, as well as the Bluetooth communications hardware.
A card docks under the brim of the SmartCap, or in the side of a SmartCap headband. Once docked, the card automatically turns on, tests itself and the cap, and begins measuring fatigue levels and sending that wirelessly to the SmartCap display. Of course, the card profile has been designed to not impede your field of vision.
In a mining or heavy industry setting, the cards typically will stay in the cab with the display and base unit.