Core Motion and the motion coprocessor
Modern iPhones include a separate, low-power coprocessor that continuously captures acceleration and motion data, even while the main system is idle. Apple exposes these values to apps through the Core Motion framework.
From the characteristic up-and-down pattern of walking, the system recognizes individual steps and counts them continuously. The app does not need to be open, as long as Motion & Fitness permission is enabled.
What it does not use
For plain step counting, iOS uses no GPS and no location data. No route is reconstructed and no path is stored, the count is based purely on the device's motion pattern.
This has a practical side effect: step counting keeps working without signal and without location access, as long as the iPhone is carried on the body.
Why values can vary slightly
The count is based on motion patterns, not on direct observation of your feet. If the iPhone is not carried on your body, for example sitting in a bag next to you or on a table, fewer or no steps get recorded accordingly.
Tips
- Carry the iPhone on your body, such as in a pocket, so motion is reliably detected.
- Check Settings, Privacy & Security, Motion & Fitness to confirm access is enabled.
- An Apple Watch on your wrist can add step data when the iPhone itself is not being carried.