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 a signal indicative of an impact. An integrated circuit is configured to determine the magnitude and direction of the impact based on the signals and operative to activate an indicator when the magnitude exceeds a selected threshold based on the direction of the impact. 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. The head injury coefficient value 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.