As a refresher, the typical automotive airbag is quite the explosive little bundle – it does not make a great travel companion. Packed tightly within its protective covering is the folded nylon airbag – but that's the inert part. A tiny igniter sits poised behind the bag waiting for the signal to set off the solid propellant (think Space Shuttle SRB). When it goes, a large volume of nitrogen gas is released at about 200 mph – the bag is fully expanded in about 1/25 of a second (it will knock your peanuts clear to first class, if you were wondering).
Common knowledge says these things simply don't blow by themselves – it takes a 12-volt charge to set airbags off (don't try it at home, kids). In any case, the Federal Aviation Administration's Office of Security and Hazardous Materials has added airbag actuators to the list of non-approved hazardous materials. The TSA wants to remind everyone to ship the "hazmat" airbags via the proper channels – do not bring them with you on a commercial airliner.
[Source: Transportation Safety Administration, Photo by TSA]