Impact sensing device and helmet incorporating the same

An impact sensing device including a plurality of accelerometers orthogonally oriented with respect to each other and attachable at a body location, each capable of producing signals indicative of impacts. An integrated circuit is configured to determine the magnitude and direction of the impacts based on the signals and operative to activate an indicator when the magnitude exceeds a first threshold based on the direction of the impact and when the magnitude exceeds a second threshold more than a selected number of times. A head injury coefficient is determined based on the magnitude and a duration of the impact, and the threshold level of acceleration is expressed in terms of a head injury coefficient value, which is determined by empirically correlating a head injury coefficient measured at the body location and a head injury coefficient measured at the center of mass of a human head resulting from an impact.