Fiat 500X 2018 Owner's Manual page 142

140 SAFETY
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