The Supplemental Restraint System, or SRS, is the system in your car that controls the automatic seatbelt restraints and the airbags. Your vehicle’s SRS is considered a passive restraint system that automatically detects things such as braking, deceleration, impact location, and if there’s a passenger in the front seat. It then sends the information to the Airbag Control Unit, which figures out which seatbelts to tighten and which airbags to activate.