Air Bag Warning Chime
WARNING: This page is about a different car, the 2007 Ford Ranger. However, it is still accessible from the selected car via links, so may be relevant.
A redundant warning chime is provided by the instrument cluster when the air bag warning indicator is not operational. The instrument cluster monitors the internal circuitry and bulb for the air bag warning indicator. If the instrument cluster receives an air bag warning indicator on request from the RCM and the instrument cluster detects a fault internally, the instrument cluster sets diagnostic trouble code (DTC) B1868 and sounds the chime.