6. What is the function of the M15's In-vehicle mode?

After turning on the In-vehicle mode, you can connect the M15 to the on-board USB port, and the M15 will power on automatically and switch to the In-vehicle mode screen when the vehicle engine starts, or power off when vehicle engine stops. (Some on-board USB port may cause ground loop interference when connected with the M15 and affect the playback, in which case you can try to use FiiO's USB isolator LA-UA1 to fix the problem)