When BSM recognizes a vehicle about to enter a blind spot, it warns you that a particular adjoining lane is not clear. Commonly, the alert comes in the form of a yellow warning light somewhere on the outboard rearview mirror on whichever side of the oncoming car is involved. It may, instead, appear on your vehicle’s A-pillar (the pillar between the windshield and either front door), driver-information display, or head-up display.