Door Latch (Door Jamb) Switches
WARNING: This page does not describe the selected car, but rather 7 other vehicles, including the 2002 GMC Yukon XL, 2002 GMC Yukon, 2002 Chevrolet Tahoe, 2002 Chevrolet Suburban, and 2002 Chevrolet Avalanche. However, it is still accessible from the selected car via links, so may be relevant.
The theft deterrent system uses the door key switch as one method in order to activate the alarm. If the BCM detects any door opening before the BCM receives a disarm input, the alarm mode activates.