Side Impact Sensor (Sis)
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.
Each SIS monitors vehicle side acceleration and velocity changes to detect side impact collisions severe enough to deploy side impact air bag modules.