Toyota C-HR 2020 Manual page 273

BSM function
The BSM function uses radar sensors to detect the following vehicles
traveling in adjacent lanes and advises the driver of the presence of
such vehicles via the indicators on the outside rear view mirrors.
Vehicles that are traveling in areas that are not visible using the out-
side rear view mirrors (the blind spots)
Vehicles that are approaching rapidly from behind in areas that are
not visible using the outside rear view mirrors (the blind spots)
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4-5. Using the driving support systems
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