Side Impact Sensor (Sis)
WARNING: This page is about a different car, the 2002 Chevrolet Monte Carlo and 2002 Chevrolet Impala. However, it is still accessible from the selected car via links, so may be relevant.
SIS monitors vehicle acceleration and velocity changes to detect side impact collisions that are severe enough to warrant deployment of side air bag. SIS is not part of deployment loop, but provides input to SDM.