A GPS tracker, or black box, is a small piece of hardware, sometimes smaller than a cellphone. It typically includes a slot for a SIM card and a plug, normally OBD-II, to connect it to a vehicle.
A GPS tracker receives a GPS signal and sends location information, along with other vehicle data, back to a fleet management system via cellular 3G, 4G LTE, CDMA or satellite networks. Using your vehicle tracking system, you can then monitor your fleet in near real time.