Turn the auxiliary key toward the front to lock, toward the back to unlock.
To lock
All doors lock automatically when the driver's door is locked using the auxiliary key.
To unlock
The driver’s door unlocks when the auxiliary key is turned briefly to the unlock position and then immediately returned to the center position.
All doors unlock when the driver's door is unlocked and the auxiliary key is held in the unlock position for one second or longer.

Door Locks
Locking, Unlocking with Request Switch, Door Handle (With the advanced keyless
function)Mazda 6 Owners Manual: Blind Spot Monitoring (BSM) Warning Indicator Lights/Display Indicator/ Blind
Spot Monitoring (BSM) Warning Beep
The Blind Spot Monitoring (BSM) or Rear Cross Traffic Alert (RCTA) system notifies
the driver of the presence of vehicles in adjacent lanes or at the rear of the vehicle
using the Blind Spot Monitoring (BSM) warning indicator light, the warning sound
and the display indicator (vehicles with mu ...
Mazda 6 Owners Manual: Rear center seat belt removal/installation
Caution
The ELR has a spring that will unwind if the retractor's cover is
removed. The spring cannot be rewound by hand. If this occurs, the ELR will
not work properly. Therefore, do not disassemble the retractor.
4SD
1. Fold the rear seat back.
2. Remove the rear package trim.
3. Re ...