1. A navigation unit for use by a user, comprising: at least one sensor; a processing unit coupled to the sensor, wherein the processing unit generates navigation-related output derived at least in part on information output by the sensor; and a wireless interface coupled to the processing unit; and wherein when the navigation-related output is transmitted from the navigation unit to a portable device being used by the user over a wireless communication link, the wireless interface transmits the navigation-related output to the portable device over the wireless communication link.