The concept of information flow applied to crash sensing in airbag systems introduced in [3] is further developed. An asymptotic formula for the amount of information available to an airbag module is obtained. This formula is applied to study the information flow in a linear spring-mass model and it gives a simple and insightful relationship between the fire time of an airbag and the accuracy of the estimation of the initial impact velocity. This relationship is in the form of an “uncertainty principle” describing the balance between the amount of time needed for the airbag sensor to estimate the severity of an impact and the uncertainty of the estimation itself. An application of the result, based on actual crash data, is presented to illustrate the analytical result.