Volkswagen Golf GTI 2016, Owner'S Manual, Page: 975 / 1341

Radar sensors
The radar sensors are behind the rear bumper on the left and right
→ Fig. 177 . They are not visible from outside the vehicle. They
monitor an area about 21 yards (20 meters) behind the vehicle as
well as the blind spots on the left and right sides of the vehicle. The
monitored area next to the vehicle is about one lane wide.
The width of the lane is not detected individually on each road, but
is preprogrammed into the system. Because of this, the indicators
may be incorrect when driving on narrow roads or driving in the
center of two lanes. Likewise, vehicles that are two lanes away from
you or stationary objects such as guard rails may also be detected
and cause a false warning.
Driving situations
Fig. 178 : Driving situation when passing with traffic behind your
vehicle. : Blind Spot Monitor indicator light in the driver side mirror.