Fiat 500 X 2016 Owner's Manual page 86

84 GETTING TO KNOW YOUR VEHICLE
Entering From The Rear
Vehicles that come up from behind your vehicle on either
side and enter the rear detection zone with a relative
speed of less than 31 mph (50 km/h).
Rear Monitoring
Overtaking Traffic
If you pass another vehicle slowly with a relative speed
less than 15 mph (25 km/h) and the vehicle remains in
the blind spot for approximately 1.5 seconds, the warning
light will be illuminated. If the difference in speed
between the two vehicles is greater than 15 mph
(25 km/h), the warning light will not illuminate.
Overtaking/Approaching