There is a weight difference in whether the airbag deploys or not. I'm pretty sure is 90 lbs. Despite your seat belt gong going off, I don't think your passenger airbag is associated with it. You'd have to look to see if the Passenger Airbag disabled light is on next to the SOS button.
'09 E90 M3 | VF620 SC tuned and coded by BPM | KW V3 | ARC Wheels w/AD08 | OnEighty Lights | AA Signature Exhaust | BMW Performance and IND trim | Recaro Profi and child seats
'13 35i M-Sport X3 | JB4 Stage 1 | BMS Intake | H&R Springs | Gloss black grill | CF Wrap and Coded by me