Functionally there may be no direct connection between Airbag and Seatbelt but yes logically there is a deep connection between Airbag and Seatbelt. As we all know that Seatbelt is Primary Restraint System and Airbag is supplementary Restraint System(SRS), Airbags always function better with the combination of Seatbelts. There are many factors behind the deployment of Airbag, deployment of Airbag is also controlled by multiple sensors car manufacturers and existing country law. As Airbag is the second line of defence so it is more obvious that it works best with the first line of defence that is Seatbelt.
Why wearing SeatBelt is so important for proper functioning of Airbag:
There are many reasons why wearing Seatbelt is so important for proper functioning of Airbag, we highlight few important points here.
Airbag can cause severe injuries when deployed if driver and co-passenger are not wearing the Seatbelt. For example if a car is travelling at 100 km. speed the driver and co-passenger are also travelling with the same speed, during sudden brake or accident the Seatbelt prevents the driver and co-passenger from double impact(forward speed impact + backward Airbag Impact) and holds them firmly.
Without the Seatbelt Airbag may miss you completely, most of the time Seatbelt holds you firmly in a position where Airbag can help you maximum.
If a driver or co-passenger wearing Seatbelts it provides sufficient time for Airbag to deploy.
Seatbelts ensure your body tightened at one place and Airbag protects your body from other objects.