GMC 2009 Sierra 1500 Crew Cab Owner's Manual page 314

Parental Control can also be turned off by inserting or
ejecting any disc, pressing the play icon on the radio DVD
display menu, or changing an ignition position.
Headphones
The RSE includes two 2-channel wireless headphones
that are dedicated to this system. Channel 1 is dedicated
to the video screen, while Channel 2 is dedicated to RSA
selections. These headphones can used to listen to the
radio, CDs, DVDs, MP3s, DVDAs, any auxiliary source
connected to A/V jacks, or the auxiliary input jack, if the
vehicle has this feature. The wireless headphones have
an On/Off button, channel 1/2 switch, and a volume
control.
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Push the power button to turn on the headphones.
An indicator light located on the headphones comes on.
If the light comes on but, there is intermittent sound
and/or static on the headphones, or if the indicator light
does not come on, the batteries might need to be
replaced. See "Battery Replacement" later in this section
for more information. Switch the headphones to Off when
not in use.
Infrared transmitters are located at the rear of the
overhead console. The headphones shut off
automatically to save the battery power if the RSE
system and RSA are shut off or if the headphones are out
of range of the transmitters for more than three minutes.
If you move too far forward or step out of the vehicle,
the headphones lose the audio signal.
The headphones automatically turns off after four hours
of continuous use.
To adjust the volume on the headphones, use the
volume control located on the right side.
For optimal audio performance, the headphones must
be worn correctly. Headphones should be worn with
headband over the top of the head for best audio
reception. The symbol L (Left) appears on the upper
left side, above the ear pad and should be positioned on
the left ear. The symbol R (Right) appears on the upper
right side, above the ear pad and should be positioned
on the right ear.