X2 on BigJims answer, I've "slammed" into things offroad pretty hard and have not set off the airbags (I even have a mangled ARB front bumper to show for it, HA). There is a sensor that detects sudden deceleration like BigJim states (like in the form of a crash or something similar...)

Fred R.

97 ZJ, 5" Long Arm Lift, Beadlocked 35's, 231/D300 Doubler, Locked Front & Rear (Narrowed HP D44 & F8.8), ARB Bull Bar & 9K winch, 1-Ton Hydro-assist steering, "Custom" body work and some other goodies... PICS