What feature uses sound or vibration to alert a driver of obstacles when reversing?

The feature that uses sound or vibration to alert a driver to obstacles while reversing is parking sensors. Most factory systems use ultrasonic proximity sensors installed in the front or rear bumper.

When reverse gear is selected, the sensors emit short ultrasonic pulses and measure the time taken for reflected echoes to return. The vehicle estimates the obstacle’s distance and warns the driver with beeps that become faster as the car approaches. Some systems add a visual display, while a few use electromagnetic sensing instead.

Parking sensors are not the same as a backup camera. A camera provides an image, whereas sensors measure proximity and give an audible or tactile warning. Cross-traffic alert is different again: it watches for moving vehicles or pedestrians approaching from the sides behind the car, usually while backing out of a space.

Sensors have limits. Narrow poles, soft objects, low obstacles, or surfaces angled away from the bumper may reflect too little sound for reliable detection. Drivers must still check mirrors and surroundings rather than treating the warning system as automatic braking.