U.S. auto safety officials will warn millions of Americans today that the air bags in over 100 vehicle models could be dangerous counterfeits, telling them to have their cars and trucks inspected as soon as possible. The unfortunate catch: Owners will have to pay -- not just for the inspection, but for the replacement of any counterfeit air bags, which could cost more than $1,000 each.

The unprecedented alert from the National Highway Traffic Safety Administration follows a lengthy investigation by auto safety and U.S. customs officials into counterfeit air bags, mostly made in China, sold as cheap replacements for factory equipment to independent mechanics and on eBay. While NHTSA says it has no reports of injuries or deaths linked to a counterfeit device, in its testing the counterfeit bags had "consistent malfunctioning," ranging from not deploying on impact to throwing metal shards.

The warning only covers vehicles which might have had their air bags replaced in the last three years by any mechanic not connected to a dealership; dealers are required to use factory certified air bags. That means not just vehicles crashed, but those whose air bags may have been stolen or used cars and trucks that may have deployed their air bags before they were bought. The advisory also applies to anyone who bought an air bag from eBay or "non-certified sources" for unusually low prices, typically about $400.

"Anytime equipment that is critical to protecting drivers and passengers fails to operate properly, it is a serious safety concern," said U.S. Transportation Secretary Ray LaHood. "We want consumers to be immediately aware of this problem and to review our safety information to see if their vehicle could be in need of inspection."

Although NHTSA says counterfeit air bags affects "less than 0.1 percent" of U.S. vehicles, that would still be roughly 3 million cars and trucks needing inspections. Officials say the problem shouldn't be that widespread, expecting only tens of thousands of fake air bags have entered use.

If your car meets those criteria and is listed in the table below showing the models affected, NHTSA asks that you call your vehicle's manufacturer at hotlines which are still being established. There's no way short of a mechanic's inspection to know whether a replacement bag is counterfeit; the faulty bags were often sold with fake insignias.

Earlier this year, federal agents charged a North Carolina man with trafficking counterfeit air bags, seizing more than 1,500 in a raid. In February, a Chinese man was sentenced to three years in federal prison after Customs officials seized more than 300 fake air bags from his auto parts company. The man, Dai Zhensong, admitted that his firm had bought original air bags from several automakers, then tore them down to make moulds for counterfeits, using badges bought from auto dealers in China. The fake bags were advertised on his company's site for $57 a piece; a real replacement air bag can run $1,000 for a driver's side unit and more for other locations.

That cost may prove the biggest hurdle for the government to overcome. Since NHTSA's action isn't a recall, vehicle owners will have to pay for the inspection, which may cost up to $100. If a fake air bag is found, owners would then have to pay for a real one to be installed. Many newer model vehicles have several air bags for passenger and side-impact protection; NHTSA hasn't yet clarified whether those types of air bags will need to be inspected as well, although most of the fake air bags found so far have been driver's side. Even when a recall is paid for by an automaker, on average about a third of the vehicles covered are never brought in for service.

We'll update this story with more information as we receive it. Here's the full list of affected models: