The side air bags are mounted in the outboard sides of the front seatbacks.
When the air bag crash sensors detect a side impact of greater than moderate force, the system inflates the side air bag only on the side in which the vehicle was hit. The side air bag inflates quickly to reduce injury to the driver or front passenger's chest caused by directly hitting interior parts such as a door or window.
For more details about air bag deployment, refer to "SRS Air Bag Deployment Criteria".
(With Front Passenger Occupant Classification System)
In addition, the front passenger side bag is designed to only deploy when the front passenger occupant classification sensor detects a passenger sitting on the front passenger's seat. For details, refer to the front passenger occupant classification system.

Front Passenger Air Bag
Curtain Air BagsMazda 6 Owners Manual: Removal/Installation
To remove the head restraint, pull it up while pressing the stop-catch.
To install the head restraint, insert the legs into the holes while pressing
the stop-catch.
WARNING
Always drive with the head restraints installed when seats are being used
and make sure they are properly installed: Dri ...
Mazda 6 Owners Manual: Dual proportioning valve inspection (without abs)
1. Connect the SSTs to the brake pipes as shown in the figure.
2. Bleed the air from the brake system.
3. Measure the fluid pressure of the master cylinder and the rear brake.
If not within the specification, replace the dual proportioning valve.
Fluid pressure
...