VST-7009V 4 In 1 Digital Car Thermometer Voltage Meter Luminous Clock Tester Detector LCD Monitor Back light 1. Easy to install and use, a perfect accessory for your car. Powered by car cigarette lighter charger or 2 x LR 44 batteries 2. Backlight will open when the clock is powered by car cigarette lighter, there would be no back light when it is powered by backup batteries 3. When it connects with car, its back light is light up and all the contents (including the time, temperature and volt) will be displayed on the LCD screen 4. Car battery voltmeter, Pedestal 180-degree revolve. Also has the function of freeze alert. Alert you to your car battery voltage and its alarm sensor notifies you of excessive or under normal voltage operations 5. Capable of switching temperature display unit Celsius Fahrenheit degree. Display accurate temperature readings in and outside of the car. The LED back light design allows you to accurately read the digits in the dark