What is HUD? Abbreviation for Head Up Display. It displays riding data on the front windshield, such as speed, RPM, water temperature, voltage, mileage, etc. It keeps drivers safe by monitoring car window data and reminds drivers of their overspeed. A variety of operation interface modes and colors can be changed freely Compatible Attention: OBDll: only available for vehicles produced after 2008. GPS MODEL: Perfect for all vehicles. Dual system: Switch freely between two models. REMARK: Data displayed in OBD2 mode is vehicle engine data. OBD2 mode only displays the battery and voltage when the vehicle is not started. Simple displayVehicle speed + Engine speed, HD display, convenient function, let you drive more comfortably during long time. (plug and play - available for 95% of cars with OBD2/GPS interface). The automatic and manual brightness adjustment mode, and easier to control the HUD. Multiple functionsAmbient decorative lighting Engine speed Error code alarm Fatigue driving alarm Alert icon Brightness sensor: The HUD can automatically adjust the brightness "according to the environment. Unit of speed: KM / H, MPH Multi-function area: speed, water temperature, battery voltage, driving distance Water temperature icon 'Voltage icon.