OBD2 VersionIt works when the car is running, and turn off when the car's ignition is off.OBD2 Display data: Speed, coolant temperature, voltage, mileage, clear faulty code.Alarms: over-speed alarm, high water temperature alarm, low voltage alarm, fault code alarm, fatigue driving alarm.Automatically turn on or off: After the engine is turned off for 30 seconds, the HUD will automatically shut down; when the engine is started, it will automatically display after 5 seconds. Our HUD with a switch, which can be turned on and off manually. If you do not drive for a long time, it is recommended to manually turn off the HUD.GPS VersionIt is compatible with all cars! And supports over-speed alarm.Product working voltage is 5V, and it is forbidden to use a voltage higher than 5V for power supply. Some vehicles voltage are highter than 5V, it doesn't matter. Our package included a usb cable, you need to plug usb cable in cigarette lighter, and connect it with HUD.Number of search satellites.Compass: N (North) E (East) W (West) S (South).Vehicle speed display,Speed unit: MPH- mile, KM/H- kilometer.Fatigue Driving Alarm: Fatigue driving alarm is 4 hours, user can freely set this time or turn off this alarm, setting time range: 1-8 hours.Please Note:OBD system is suitable for most cars after 2007.OBD2 model can work for OBD2 gasoline vehicles produced after 2004 in USA, and OBD2 gasoline vehicles produced after 2008 in other countries.OBD2 model is not applicable for the following cars:Package List:1 x HUD1 x Manual1 x OBD Cable or GPS USB Cable1 x Reflective film1 x3M Sticker