Automatic speed dependent door locks/unlocks. A thing that plugs into the OBD2 diagnostic connector and reads the speed of the car from the electronic control unit, then gives a signal to close the central lock of the four doors of the car. A useful device for those who don't have this feature from the factory and who often carry children in the car who might inadvertently open a door while driving. When the speed reaches 9 mph, the doors will automatically lock and open again when the engine is shut off. You can also unlock the doors by forcibly pressing a button.