It 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 , 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. It will automatically alarm if overspeed, so it can from looking down the speedometer and drive safely. You can freely set this value. Setting Speed range: 30-250KM/H. Screen Size: 3.2 inches Display Type: Windshield Projector Dimension: 8.6x3.7x1.6cm Easy to install Step1: Insert the OBD socket connector. Step2: The wire is stuffed into the A-pillar sealing strip. Step3: Connect one end of the obd interface to the HUD and place the HUD to a suitable position. Colour:Photo Color Material:ABS Package Contents: 1 x Car Electronics HUD Projector Only the above package content, other products are not included. Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.