Answer: Open this page on your phone — it reads your device motion sensors live and graphs the accelerometer output in real time.
Live motion and tilt readout — does your phone's sensor keep up?
The page uses the browser's DeviceMotion and DeviceOrientation APIs to read your phone's motion sensors directly — no app install needed. On iOS you must tap a button to grant motion permission before the sensor readout starts. All processing happens locally in your browser, so nothing is uploaded.
A failing accelerometer causes auto-rotate to stop working, screen orientation to stick, and fitness or game apps to track motion incorrectly. Comparing the live 3-axis readout against how you are actually moving the phone reveals dead, noisy, or stuck sensor axes. A flat-line value on one axis while shaking the phone indicates a hardware fault.
Most desktops have no accelerometer or gyroscope, so the sensors report unavailable or zero values. The test is designed for phones and tablets, where motion sensors are standard. Opening it on a desktop is useful mainly to confirm the page loads, not to test sensors.
The page listens to two standard web APIs. devicemotion reports acceleration in m/s² along the X (left–right), Y (front–back) and Z (up–down) axes — including gravity, which is why a phone lying flat shows ≈9.8 on Z. deviceorientation reports the tilt in degrees: alpha is rotation around the vertical axis (compass heading), beta is tipping toward/away from you, and gamma is tilting left/right.
How to read it: hold the phone flat and watch the bars settle, then tilt it slowly onto each edge — the ~9.8 m/s² of gravity should slide from axis to axis smoothly. Shake it: the peak readout should jump well past 20 m/s². A sensor that freezes at fixed values, never settles near 9.8 on the down-facing axis, or drifts wildly while the phone is still on a table is faulty — and it will break auto-rotate, step counting and landscape games until repaired.
Why does iOS ask for permission? Apple requires an explicit user gesture before a page can read motion sensors. When you press Start on iPhone, Safari shows a "Motion & Orientation Access" prompt — tap Allow. If you denied it earlier, reopen the page and press Start again, or reset the choice in Settings → Safari → Advanced → Feature Flags / website data.
The numbers don't change when I rotate the phone. First check that auto-rotate itself isn't locked in your quick-settings toggle — that lock only affects the UI, but it's a quick sanity check. Then confirm orientation lock isn't enabled in the browser. If the beta/gamma tiles stay frozen on every axis while X/Y/Z move, the gyroscope is reporting nothing: that's a hardware fault worth a service visit.