GMC 2007 Sierra - Manual (Page 121)

To unlock the door from the outside, use the
Remote Keyless Entry (RKE) transmitter or the key.
To unlock or lock the
door from the inside,
slide the manual
lever forward or
rearward.
Power Door Locks
If your vehicle has this
power door lock switch,
press the raised side
of the switch, with
the lock symbol,
on either front door to
lock all the doors
at once.
Press the recessed side of the switch with the
unlock symbol, to unlock all the doors at once.
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