Audi side assist
The Audi side assist lane-changing assistant helps the driver to change lanes at driving speeds of 15 km/h (9.3 mph) and faster.
It uses two rear-mounted radar sensors with a scanning range of roughly 70 meters (229.7 ft). If the system detects a vehicle located in the blind spot or approaching quickly from the rear, a warning LED is lit in the housing of the relevant exterior mirror. If the driver activates the turn signal anyway, the LED flashes several times in rapid succession.
This is part of the city assistance package with option id PCM and side assist pacakge with option id PCH