The blind spot monitor or 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.

A blind spot in a vehicle or vehicle blind spot is an area around the vehicle that cannot be directly seen by the driver while at the controls, under existing circumstances. In transport, driver visibility is the maximum distance at which the driver of a vehicle can see and identify prominent objects around the vehicle. Visibility is primarily determined by weather conditions and by a vehicle's design. The parts of a vehicle that influence visibility include the windshield, the dashboard and the pillars. Good driver visibility is essential to safe road traffic.