US Patent 10981504 Vehicle back door and vehicle warning method and system

A vehicle back door includes a back door main body having a window opening and a back door pane attached to the window opening. The back door main body has a speaker. The speaker is disposed below the back door pane and the angle α1 formed by a vehicle height direction axis and a central axis of the speaker is set to a value smaller than the inclination angle α2 of the back door pane with respect to the vehicle height direction axis. The sound emitted by the speaker is reflected by the back door pane and then transmitted to the front part of the vehicle interior.