I’m primarily talking about stuff like step counters, but also health apps measuring your heart rate, how many stairs you take, the length of your steps, and so on. I’m honest when you tell me to explain it to me like I’m five years old, this one boggles my mind.
Your phone has something called an accelerometer in it, it’s a sensor that can tell the orientation of the device. It tracks your rhythm with the phone swinging left and right to tell when you take a step or climbed some stairs. Many apps also use your GPS location to give you a rough estimate if your accelerometer isn’t up for it.