Chrysler 300 2018 Owner's Manual page 156

154 SAFETY
The BSM system monitors the detection zone from three
different entry points (side, rear, front) while driving to see
if an alert is necessary. The BSM system will issue an alert
during these types of zone entries.
Entering From The Side
Vehicles that move into your adjacent lanes from either
side of the vehicle.
Side Monitoring
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