Cadillac DTS 2011 Owner's Manual page 90

Driver Side shown, Passenger Side similar
The seat-mounted side impact airbags for the driver and
right front passenger are in the side of the seatbacks
closest to the door.
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Driver Side shown, Passenger Side similar
If the vehicle has roof-rail airbags for the driver, right
front passenger, and second row outboard passengers,
they are in the ceiling above the side windows.