An energy-efficient acceleration measurement system is presented. The system includes an accelerometer, responsive to acceleration of the system, for providing an accelerometer output signal having a magnitude indicative of at least one component of the acceleration. A motion detector is responsive to the accelerometer output signal, and provides a processor interrupt signal, but only if the magnitude of acceleration reaches a threshold. The processor, responsive to the processor interrupt signal, measures the acceleration with higher accuracy than the motion detector is capable of, but in a way that consumes more power than was needed by the motion detector.