blind spot

The vehicle blind spot monitor or simply blind-spot monitoring 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.
Vehicle blind spot (VBS) monitors may do more than monitor the sides and rear of the vehicle. They may also include "Rear Cross-Traffic Alert", "which alerts drivers backing out of a parking space when traffic is approaching from the sides."

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