Will your car's air bags work when they're supposed to? Probably - but not necessarily.

They may have become too "smart" for their own good - and ours.

All '04 model year and newer cars have at least driver and passenger-side air bags - as mandated by federal law. Most '04 and newer models also have air bags built into the upper seat bolsters or doors to protect against side impact injuries.

Many current-year models even have "curtain" air bags built into the roof area to protect your noggin in the event of a higher-up hit or rollover-type accident.

There are even knee air bags now.

Most 2011 model cars have a minimum of four air bags: Driver and front seat passenger plus front seat side-impact bags. Several current-year cars have as many as eight air bags (or even more).

That's a a lot of air bags.

Most of these air bags are also "smart" - meaning they are tied into sensors of one type or another that provide information to help the Supplemental Restraint System's main control unit determine when each bag should deploy - and with how much force. For example, smart air bags can - in theory - tell if there's no one occupying the passenger-side seat and turn themselves off so the bag doesn't deploy in the event of an accident. This is not so much a safety issue as a cost issue. Replacing air bags - which are a one-shot/can't re-use them deal - can be hugely expensive. If both driver and front seat passenger bags deploy, the steering wheel and dashboard must usually be replaced, too - in addition to the bags themselves. That can add up to $2,000 (or more) before you even start fixing bent fenders. In older cars whose retail value has dropped to less than $5,000 an otherwise fairly minor - and economically fixable - repair becomes a "total" because the cost to fix the bags and related interior damage already adds up to nearly 50 percent of the car's market value - the point at which most insurers will throw the car away rather than pay to have it fixed. So, by cutting down on unnecessary air bag deployments - such as a passenger side bag going off when there's no one sitting in the passenger seat - the "smart" system could save the car's life.

Smart air bags can also adjust the rate and force of deployment - adjusting these parameters to take into account an unbuckled passenger, for example. (The bag needs to deploy with more force - and faster -to be effective in that case.)

There are also weight sensors built into many of these systems that can detect the presence of a toddler or small child - and either decrease the force of the bag's deployment or turn it off entirely to prevent an injury. A few of the really advanced "smart" air bags can even tell if a person is positioned too close to the air bag - which could result in severe facial injury such as torn retinas, etc. if an accident were to occur and the bag were to deploy full-force.

But here's the catch:

All these sensors have added greatly to the complexity of modern Supplemental Restraint Systems -the fancy name for air bags - and it's an engineering axiom that the greater the complexity of any mechanical system, the greater the odds of an eventual failure.

And the sooner such failures are likely to occur.

The Space Shuttle is more likely to break down than a '78 F-150. And when it does break down, the fix is not going to be easy - or cheap.

The potential for a problem or fault developing also increases over time, as the vehicle ages - just as you are statistically more likely to croak of a heart attack if you're 50 vs. 25.

All the components of the Supplemental Restraint System are part of the car and go where it goes and suffer what it suffers. Just like the once rich-looking, crack-free dashboard that's been oxidized and crinkled by the sun - and those formerly shiny fenders that now look faded and washed out after a few seasons of being sloshed with icy slush - all the intricate parts of the SRS system are subjected to extremes of heat and cold, as well as repeated exposure to moisture and humidity and continuous on-off operating cycles. Sensitive components experience almost constant vibration, bumps - even a jarring impact once in awhile, when you fall into a canyon-like pothole.

These "environmental factors" corrode and weaken connections, fray wires and in general beat up all the bits and pieces pretty effectively. Even stuff that leads a sheltered life - think, for instance of a TV parked in your climate controlled living room that never moves, never gets too cold (or hot)... eventually, it fritzes out, too.

We won't know the full story for a few years yet because air bags are still new technology. Even the old "dumb" air bags - the first generation SRS systems - are only about 15 years old now. The "smart" systems haven't been out long enough for an evaluation to be made of how well (or not) they'll hold up over time.

We do know, however, that many of these system have already malfunctioned in one respect of another - warning lights coming on when they shouldn't; systems turning themselves on (or off) based on faulty sensor data - stuff like that. A few have deployed for no reason (well, no crash) and with no warning - which made for an exciting day for the drivers of those cars.

Here's something to think about a bit: If you read the fine print in your owner's manual, you'll see that most manufacturers recommend having the entire SRS system checked and serviced - usually at the ten year mark. A few recommend having all the components replaced at 10-12 years.

How many second or third owners of 10-15 year-old beaters are going to take said beater in to have $3,000 (or even $500) worth of service performed on the air bags? Anyone who has owned an older car knows that unless the thing isn't running at all, the last place it is going is the $70-per-hour dealership. Most people will just keep right on driving until the wheels fall off.

Or the air bag goes off unexpectedly. Or doesn't go off when it should.

The lawyers are going to have a party... .