RepairPal Certified shops can diagnose and repair your 2013 BMW 528i. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.
How much does that 'someone' weigh? IF it is a child , they may not be heavy/large enough , and for safety reasons the airbag is turned off. Another possibility is that a sensor is failed. TESTING would be the safest way to know.