When people want to know how much they have walked in a day, many check the pedometer on their smartphones.

So, how exactly does a smartphone count steps?

You might assume it simply counts vibrations, but smartphones are subjected to vibrations other than just those caused by walking.
Vibrations occur in all sorts of situations during daily life.

To accurately isolate the movement associated with walking from all this other activity, smartphones utilize an “accelerometer” and a “gyro sensor.”

First, the accelerometer is a sensor that detects the smartphone’s movement.
In other words, it tracks the speed and nature of the movement.
By isolating only the vibrations that move continuously up and down—perpendicular to the ground—at a consistent speed and range, the device identifies “steps.”

However, the orientation and angle of the smartphone vary while a person walks.

You might move your hand while holding it, or the phone might shift to various angles inside a pocket or backpack.
By using the gyro sensor to detect these changes in angle and orientation, the smartphone can constantly determine which direction is “perpendicular to the ground,” regardless of how it is positioned.