Crash sensors for use in deploying air bags operate in an environment of severe vibrations, not only along the longitudinal axis of the sensor, but also in the transverse vertical and lateral axes. These vibrations can have a detrimental effect on some crash sensor designs. Various methods using Fourier analysis have failed to provide a characterization of cross-axis vibrations. This is due, in part, to phase shifts in the cross-axis oscillations. A technique using shock spectrum analysis has been developed which can be used to characterize these vibrations. This work has led to the development of a specification for laboratory testing of the sensitivity of a sensor to cross-axis vibrations.This paper presents the underlying theoretical basis for the shock spectrum technique, the results of applying this technique to a library of crash data, and a recommended specification for laboratory sensor testing for sensors mounted in the crush zone and non-crush zone.