It could happen for two reasons

1. The car's body control module(BCM) has a software glitch in the code which causes the light to come on even though nothing is wrong. I've seen some cars check engine lights come on but the car still runs fine so I assume it's the same root cause.

2. One of the airbag sensors might be faulty, most likely the passenger side.

Either way, you should mention this to the SC once you go for the 1000km service just to be safe.

sometimes no passengger also got sound ..

I know this problem...You need tape down the metal behind the seat..(if you can fold back seat). The metal is similar like boot opening (u shape)