Pedometers in general
Common electronic pedometers (e.g. activity trackers) are equipped with an digital triple-axis accelerometer (3-DOF) which measures the acceleration of the three directions (X, Y, Z). With an algorithm parsing the values in the background, steps can be detected on a specific pattern. The accuracy of detection mostly depends on a good algorithm. Some trackers additionally use multiple sensors such as an accelerometer and a gyroscope (6-DOF or even more) for precise determination on the hardware side.
You can find plenty information about accelerometers on the internet (if you’re interested in this topic).
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