A Sensor to determine the location on the Vehicle of Impact and the severity of the Impact to determine if and which Air Bags should be deployed.

SENSOR-SIDE AIR BAG Air Bag Impact Sensor

Fits Crosstrek, Forester, Impreza, STI, WRX

Air Bag Crash Sensor
An airbag or SRS light can sometimes indicate a problem with the impact sensor on your Subaru , particularly if it's been involved in a collision—at any speed. Have a technician inspect your vehicle's crash sensor.