The technology for a pedometer includes a mechanical sensor and software to count steps. Early forms used a mechanical switch to detect steps together with a simple counter. If one shakes these devices, one hears a lead ball sliding back and forth, or a pendulum striking stops as it swings. Today advanced step counters rely on MEMS inertial sensors and sophisticated software to detect steps. These MEMS sensors have either 1-, 2- or 3-axis detection of acceleration. The use of MEMS inertial sensors permits more accurate detection of steps and fewer false positives. The software technology used to interpret the output of the inertial sensor and “make sense of accurate steps” varies widely. The problem is compounded by the fact that in modern day-to-day life, such step-counters are expected to count accurately on locations where users frequently carry their devices (attached to the belt, shirt/pants pocket, hand bag, backpack).
The accuracy of step counters varies widely between devices. Typically, step counters are reasonably accurate at a walking pace on a flat surface if the device is placed in its optimal position (usually vertically on the belt clip). Although traditional step counters are affected dramatically when placed at different angles and locations, recent advances have made them more robust to those non-ideal placements. Still, most step counters falsely count steps when a user is driving a car or makes other habitual motions that the device encounters throughout the day. This error accumulates for users with moderate commutes to work. Accuracy also depends on the step-length the user enters.
Best pedometers are accurate to within ± 5% error.