The blind spot monitor is a vehicle-based sensor device that detects other vehicles located to the driver’s side and rear. Warnings can be visual, audible, vibrating, or tactile.
Optical blind spot detector on side mirrors
However, blind spot monitors are an option that may do more than monitor the sides and rear of the vehicle. They may also include “Cross Traffic Alert”, “which alerts drivers backing out of a parking space when traffic is approaching from the sides.
Car Safety 