DeviceMotionEvent

DeviceMotionEvent is a web platform interface that provides access to the device’s motion sensors, delivering data about acceleration and rotation through motion events. On supported devices, web pages can listen for these events by registering a handler for the devicemotion event on the window.

The DeviceMotionEvent interface exposes several properties. Acceleration contains the rate of change of velocity along the device’s x, y, and z axes, measured in meters per second squared, but can be null if not available. AccelerationIncludingGravity provides the same measurements with gravity included. RotationRate reports the rate of rotation around the device’s alpha, beta, and gamma axes, typically in degrees per second. Interval indicates the time in milliseconds between successive samples. Not all properties are guaranteed to be provided on every device.

Usage typically involves adding an event listener, for example. When a devicemotion event fires, developers can read event.acceleration, event.accelerationIncludingGravity, event.rotationRate, and event.interval, while guarding against null values.

Permissions and privacy considerations vary by platform. On iOS devices running iOS 13 and later, access to motion data requires explicit user permission obtained via DeviceMotionEvent.requestPermission() after a user gesture; elsewhere, a secure context (HTTPS) is usually required. Some browsers may restrict or limit data access or throttle frequency. Feature detection is recommended to avoid errors, using checks like typeof DeviceMotionEvent !== 'undefined' and, where applicable, the requestPermission method.

Applications include motion-aware games, fitness or activity tracking, and user interface adaptations based on movement. DeviceMotionEvent is closely related to DeviceOrientationEvent, which provides orientation data without necessarily combining translation or rotation rates.