Up for sale is a good used SRS sensor.  This is for Saab 9-3's 2003 

Srs Sensor - Genuine SAAB 12791067  - all will interchange.

This is a good used unit.  These units list as no longer available from Saab!  Before they became no longer available, they cost $175.10 each! 

I had a problem with one of these in my personal car! (a 2004 Saab 9-3 aero) - When ever I hit bumps in the road, or honked the horn, the "Bing bong" sound would go off, the exclamation point in the center of the cluster would light up, and the "AIR BAG" light would light up.  About 10 seconds later, this would self correct and the lights would go off. then a minute later, this would happen again.

If you will note, the horns point directly AT these sensors.  and they also are sensitive to vibrations.  So a sensor that is starting to go bad, this seems to be triggers for the air bag light.  For sure diagnosis?  Hook up to the tech2 Saab tool, and it will tell you what your air bag code is for.  Otherwise, if you are having air-bag lights, this is a shot in the dark.  But... Apparently these sensors going bad IS a very common problem.