Cadillac 2002 DeVille Owner's Manual page 186

Horn Sounds at Lock
This feature sounds the horn once when the remote
keyless entry transmitter is used to lock the vehicle.
All doors must be closed for this feature to work.
Programmable Modes
Mode 1: ON
Mode 2: OFF
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Before your vehicle was shipped from the factory, it was
programmed to Mode 2. The mode to which the vehicle
was programmed may have been changed since it left
the factory. To determine the mode to which the vehicle
is programmed or to program the vehicle to a different
mode, do the following:
1. Enter FEATURE PROGRAMMING following the
instructions listed previously.
2. Press the down arrow on the INFO button until
HORN SOUNDS AT LOCK appears on the
DIC display.
3. To turn on the feature, press the ON/OFF button
until ON appears on the DIC display. To turn it off,
press the ON/OFF button until OFF appears on
the display.
The mode you selected is now set. You can either exit
the programming mode by following the instructions
later in this section or program the next feature available
on your vehicle.