If equipped, there is a small convex mirror built into the upper and outer corner of the driver outside mirror. It can show objects that may be in the vehicle's blind zone.
Driving with the Blind Spot Mirror
Actual Mirror View
When the approaching vehicle is a long distance away, the image in the main mirror is small and near the inboard edge of the mirror. As the vehicle gets closer, the image in the main mirror gets larger and moves outboard. As the vehicle enters the blind zone, the image transitions from the main mirror to the blind spot mirror. When the vehicle is in the blind zone, the image only appears in the blind spot mirror.