The air bag sensors are designed to only trigger in a head-on crash over a specific speed. 10-20 degrees off-center from head on will trigger them too. In a side impact, the air bag would do more harm than good.
Two sensors must trip at exactly the same time. Either front sensor must trip AND the "safing" sensor inside the computer. The computer and sensors must be mounted in their proper positions to work as designed. Changing the angle these parts are mounted in will change the speeds they trip at. A good lawyer will have a field day when he finds signs of that kind of modification.
To tell if your system is ready to function, watch the red "SRS" or "Airbag" light when you turn on the ignition switch. It will light up for seven seconds, then turn off. If it never comes on, or it stays on, there is a problem. When it stays on, the system is disarmed and will not pop in a crash.
The most common failure is the "clockspring" under the steering wheel. That's a wound-up ribbon cable making solid electrical connections. Nine volts is enough to light off the rocket fuel in the airbag. A static electricity shock that you can feel is at least 3000 volts. To prevent static electricity from popping the bag, every electrical connector has shorting bars that activate when the plugs are disconnected. However, if the clockspring wiring breaks, there is an open connection that is susceptible to static electricity. The wiring is monitored by the computer so when it breaks, the red warning light is turned on and the system won't work. If the rest of the wires in the clockspring break, you will not have a horn, and the cruise control won't work if you have that option.
On older cars, seat belt use was not required for the airbag system to work. Many newer cars have an explosive charge built into the latch that tightens the belt when the airbag pops, but I don't know if you have to be wearing the belt for the airbag to work.
If you ever are in a crash where the bag pops, a common injury is rug burn from the canvas bag rubbing against your arms. After that, your eyes will burn from the gas. It's just nitrogen oxide, the remains of the burning rocket fuel, sodium azide. This is the same gas that can burn your eyes from diesel truck exhaust. Other than the temporary burning, it's harmless.
Monday, March 30th, 2009 AT 5:24 AM