If you are contemplating installing a backup warning alarm in a 2001 Deville DHS/DTS and adjacent years here is a hint.
The alarm would be the type that is integrated with a backup bulb, NAPA part
3290.To gain access to the existing bulb you need to remove the trunk deck liner which is held in place with black plastic retainers. There are about a dozen of them and it would be wise to have a few available incase you inadvertently destroy the existing ones while removing them. I was lucky and was able to reuse all of the existing retainers.
The backup lighting unit is held in place with nuts located behind the liner. Upon the removal you can then open the assembly, remove either the left or right bulb and insert the NAPA alarm bulb.
Reassemble and then go to the dash programming mode and turn off the lights flash on remote lock and the same with remote unlock. The reason being the backup alarm circuitry causes the exterior lights to continue to cycle the flashing if not turned off.
Now whenever the ignition is on and you put the car in reverse gear the alarm will sound and hopefully younguns will get out of the way before you backup.