GMC 2009 Envoy Denali Owner's Manual page 63

Driver Side shown, Passenger Side similar
The roof-rail airbags for the driver, right front passenger,
and second row outboard passengers are in the
ceiling above the side windows.
CAUTION:
{
If something is between an occupant and an
airbag, the airbag might not inflate properly or it
might force the object into that person causing
severe injury or even death. The path of an
inflating airbag must be kept clear. Do not put
anything between an occupant and an airbag, and
do not attach or put anything on the steering
wheel hub or on or near any other airbag
covering.
Never secure anything to the roof of a vehicle with
roof-rail airbags by routing a rope or tie down
through any door or window opening. If you do,
the path of an inflating roof-rail airbag will be
blocked.
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