Sony CDX-GT550UI Operating Instructions Manual page 3

Warning if your car's ignition has no
ACC position
Be sure to set the Auto Off function (page 19).
The unit will shut off completely and
automatically in the set time after the unit is
turned off, which prevents battery drain.
If you do not set the Auto Off function, press
and hold (SOURCE/OFF) until the display
disappears each time you turn the ignition off.
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