These locks are intended to help prevent children from accidentally opening the rear doors. Use them on both rear doors whenever a child rides in the rear seat of the vehicle.
If you slide the child safety lock to the lock position before closing that door, the door cannot be opened from the inside. The door can only be opened by pulling the outside handle.

Locking, Unlocking with Door- Lock Knob
Trunk LidMazda 6 Owners Manual: Disconnection of the negative battery cable
Before beginning any work, turn the ignition switch to LOCK position,
then disconnect the negative battery cable and wait for more than 1 minute
to allow the backup power supply of the SAS unit to deplete its stored
power. Disconnecting the battery cable will delete the memories of the
...
Mazda 6 Owners Manual: Operating Tips for Audio System
WARNING
Always adjust the audio while the vehicle is stopped: Do not adjust
the audio control switches while driving the vehicle. Adjusting the audio while
driving the vehicle is dangerous as it could distract your attention from the vehicle
operation which could lead to a serious accident. E ...