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
Doors and LocksContact Authorized Mazda Dealer and Have Vehicle Inspected
If any of the following warning lights or the indicator light turns on/flashes, the system may
have a malfunction. Contact an Authorized Mazda Dealer to have your vehicle
inspected.
...
System
The system operates only when the driver
is in the vehicle or within operational
range while the key is being carried.
NOTE
When the battery power is low, or in
places where there are high-intensity radio
waves or noise, the operational range
may become narrower or the system may
not operate ...
Instrument Cluster Inspection
Speedometer
Using a speedometer tester
CAUTION:
When only the front or the rear wheels are driven using a speedometer tester,
the ABS or DSC may determine that the vehicle speed signal is in error and the
engine cannot be stopped by the normal operation. If the engine cannot be stopp ...