The device does not power off automatically after the vehicle is turned off. How can I fix this?

This is related to the power supply policy of the vehicle head unit's USB port. Different vehicles have different power supply logic: some cut the power as soon as the vehicle is turned off, some do not switch off the USB port's power immediately after shutdown, and some keep supplying power continuously. If this bothers you, please unplug the device manually after getting out of the car, or simply turn off the Bluetooth connection on your phone.