If your vehicle rapidly closes in on the vehicle ahead because the vehicle applies the brakes suddenly while you are traveling in headway control, the warning sound activates and the brake warning is indicated in the display. Always verify the safety of the surrounding area and depress the brake pedal while keeping a safer distance from the vehicle ahead.
Additionally, always keep a safer distance from the vehicles behind you.

Mazda Radar Cruise Control (MRCC) Display Indication
Setting the SystemMazda 6 Owners Manual: Combine sensor inspection
Caution
Be careful and do not allow the lateral-G sensor to fall. If by
chance it is subjected to strong impact, replace it.
1. Connect the connector.
2. Turn ignition switch on, verify the voltage between terminals B and E
under the following conditions.
If not within the specifi ...
Mazda 6 Owners Manual: Smart City Brake Support (SCBS)
The Smart City Brake Support (SCBS) system alerts the driver of a possible collision
using an indication in the display and a warning sound when the Forward Sensing
Camera (FSC) detects a vehicle ahead and determines that a collision with a vehicle
ahead is unavoidable while the vehicle is bei ...