On many cars, the airbag module has to be replaced after it has operated. Others require a scan tool to reset it so it works again and can only be reset a couple of times before requiring replacement. You'll get an idiot light until the module is replaced or reset.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)