Always use the automatic locking mode to keep the child-restraint system from shifting to an unsafe position in the event of an accident. To enable seat belt automatic locking mode, pull it all the way out and connect it as instructed on the child-restraint system. It will retract down to the child-restraint system and stay locked on it. See the section on child restraint.
Emergency Locking Mode
Seat BeltMazda 6 Owners Manual: Lane Departure Warning
If the system determines that the vehicle may deviate from its lane, the lane
departure warning (beep sound, rumble sound*1, or steering wheel vibration) is activated
and the direction in which the system determines that the vehicle may deviate is
indicated in the multi-information display and ...
Mazda 6 Owners Manual: Rear door lock actuator inspection
Door Lock Actuator
1. Disconnect the front door lock actuator connector.
2. Apply battery positive voltage to the front door lock actuator terminals
and inspect the operation of the front door lock actuator.
If not as specified, replace the front door lock actuator.
With double locking ...