The curtain air bags are mounted in the front and rear window pillars, and the roof edge along both sides.
When the air bag crash sensors detect a side impact of greater than moderate force, the curtain air bag inflates quickly and helps to reduce injury mainly to the rear outboard passenger's head 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".
In a side impact:
Greater than moderate impact to one side of the vehicle will cause the curtain air bag on that side only to inflate.

(With Front Passenger Occupant Classification System) In a roll-over:
In response to a vehicle roll-over, both curtain air bags inflate.

Warning Light/Beep
A system malfunction or operation conditions are indicated by a warning.Refer to Warning/Indicator Lights. Refer to Warning Sound is Activated.
Side Air Bags
SRS Air Bag Deployment CriteriaMazda 6 Owners Manual: Lane-Change Signals and Three-Flash Turn Signal
Lane-Change Signals
Move the lever halfway toward the direction of the lane change—until the indicator
flashes— and hold it there. It will return to the off position when released.
Three-Flash Turn Signal
After releasing the turn signal lever, the turn signal indicator flashes three
times ...
Mazda 6 Owners Manual: Cruise control switch inspection
1. Disconnect the negative battery cable.
2. Remove the driver-side air bag module. (See DRIVER-SIDE AIR BAG MODULE
REMOVAL/INSTALLATION.)
3. Disconnect the cruise control switch connector.
4. Inspect for resistance and continuity between the cruise control switch
terminals using an ohmmeter. ...