Did you guys enable the Auto-Lock function? The function that car will auto lock when you walk away from it.
Sometimes when I at home, I want the car remain unlocked, is there any method?
Cause everytime I walk away, it will auto lock. Even I press unlock from key fob, after certain time, it is locked again.
From Mazda manual
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Auto re-lock function
After unlocking with the request switch, all doors and the liftgate will automatically lock if any of the following operations are not performed within about 30 seconds. If your vehicle has a theft-deterrent system, the hazard warning lights will flash for confirmation.
The time required for the doors to lock automatically can be changed.
Refer to Personalisation Features (Search).
Opening a door or the liftgate.
Switching the ignition to any position other than off.
I use this method, press unlock from key fob, open and close the door. It will still lock itself again.

keep key fob inside the car.