Mazda 3 Owner's Manual page 237

When Driving
Blind Spot Monitoring (BSM) System
NOTE
Under the following conditions, the system may be unable to detect vehicles, or detection
may be delayed.
The vehicle is reversed at a speed of 12 km/h or faster
The radar is obstructed by objects such as a large vehicle parked adjacently or by a wall.
(Reverse vehicle to position in which radar is not obstructed.)
A vehicle approaches from straight behind
The vehicle is parked at a highly acute angle
Immediately after the system has been activated by pressing the Blind Spot Monitoring
(BSM) OFF switch again after it has been turned off (Blind Spot Monitoring (BSM) OFF
indicator light in instrument cluster illuminates) by pressing the switch.
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Your vehicle
Your vehicle
Your vehicle