Function Description

The BSW system can help alert the driver of other vehicles in adjacent lanes when changing lanes.
The BSW system uses side radar installed near the rear bumper to detect vehicles in an adjacent lane.
The side radar can detect vehicles on either side of vehicle within the detection zone shown in figure below.
This detection zone starts from the outside mirror of vehicle and extends approximately 10 ft (3.0 m) behind the rear bumper, and approximately 10 ft (3.0 m) sideways.
The BSW system operates above approximately 32 km/h (20 MPH).
If the side radar detects vehicles in the detection zone, the BSW/BSI indicator illuminates.

Fig 1: Overview Of BSW System Control (Indicator On)
Courtesy of NISSAN NORTH AMERICA, INC.
If the driver then activates the turn signal, a buzzer will sound twice and the BSW/BSI indicator will blink.

NOTE: A buzzer sounds if the side radar have already detected vehicles when the driver activates the turn signal. If a vehicle comes into the detection zone after the driver activates the turn signal, then only the BSW/BSI indicator blinks and no buzzer sounds.

Fig 2: Overview Of BSW System Control (Buzzer, Indicator Blink)

Courtesy of NISSAN NORTH AMERICA, INC.