GMC Sierra Denali 2009 Owner's Manual page 262

Parental Control
The RSE system may have a Parental Control feature,
depending on which radio the vehicle has. To start
Parental Control, press and hold the radio power button
for more than two seconds to stop all system features
such as: radio, video screen, RSA, DVD and/or CD.
While Parental Control is on, a padlock icon displays.
The radio can be turned back on with a single press of
the power button, but the RSE system will remain
under Parental Control.
To turn Parental Control off, press and hold the radio
power button for more than two seconds. The RSE
returns from where it was previously left and the padlock
icon disappears from the radio display.
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.
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Headphones
The RSE includes two 2-channel wireless headphones
that are dedicated to this system. Channel 1 is
dedicated to the DVD player, while Channel 2 is
dedicated to RSA selections. These headphones can be
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.