"The device can display turn arrows, distance to the next turn, current speed, speed limit and estimated time of arrival. It also recommends the best lane for driving and warns of potential traffic delays, as well as upcoming safety camera locations.

HUD receives navigation info from a Bluetooth-enabled smartphone — iPhone, Android or Windows Phone 8 — running a Garmin StreetPilot1 or NAVIGON app. HUD provides visual information and well as verbal turn-by-turn directions, either through smartphone speaker or Bluetooth-connected car stereo system. "

http://mashable.com/2013/07/08/garmin-portable-hud/