Cadillac 2005 XLR Owner's Manual page 188

You can select to not have the horn sound when the
passive lock occurs. If you choose this setting, the doors
will automatically lock eight seconds after you turn the
ignition off, remove the keyless access transmitter
from the interior of the vehicle and close both doors.
You can also select to have the horn sound once when
the passive lock occurs. If you choose this setting,
the doors will automatically lock and the horn will chirp
eight seconds after you turn the ignition off, remove
the keyless access transmitter from the interior of the
vehicle and close both doors.
If you are parking in a quiet area and do not want the
horn to sound when the doors lock, press the lock button
on the keyless access transmitter immediately after
removing it from the interior and closing the doors. This
will lock the doors and cancel the passive locking for
this ignition cycle.
The DIC will display PASSIVE LOCKING OFF, SILENT
PASSIVE LOCK or HORN AT PASSIVE LOCK.
Press the OPTIONS button to change the setting.
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Passive Unlocking
This feature allows you to select which doors will
automatically unlock when you approach and open the
driver's door with your keyless access transmitter.
You can choose to have the driver's door unlock or both
doors unlock. See Door Locks on page 2-9 for more
information.
The DIC will display PASSIVE UNLK DRIVER or
PASSIVE UNLK BOTH. Press the OPTIONS button to
change this setting.
Auto Unlock
This feature automatically unlocks either the driver's
door or both doors, depending on the setting, when the
shift lever is moved to PARK (P).
The DIC will display AUTO UNLOCK OFF, AUTO
UNLOCK DRIVER or AUTO UNLOCK BOTH. Press the
OPTIONS button to change the setting.