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Expo DeviceMotion iconExpo DeviceMotion

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A library that provides access to a device's motion and orientation sensors.

Android
iOS
Web

DeviceMotion from expo-sensors provides access to the device motion and orientation sensors. All data is presented in terms of three axes that run through a device. According to portrait orientation: X runs from left to right, Y from bottom to top and Z perpendicularly through the screen from back to front.

Installation

Terminal
npx expo install expo-sensors

If you're installing this in a bare React Native app, you should also follow these additional installation instructions.

Configuration in app.json/app.config.js

You can configure DeviceMotion from expo-sensor using its built-in config plugin if you use config plugins in your project (EAS Build or npx expo run:[android|ios]). The plugin allows you to configure various properties that cannot be set at runtime and require building a new app binary to take effect.

Example app.json with config plugin

app.json
{
  "expo": {
    "plugins": [
      [
        "expo-sensors",
        {
          "motionPermission": "Allow $(PRODUCT_NAME) to access your device motion."
        }
      ]
    ]
  }
}

Configurable properties

NameDefaultDescription
motionPermission"Allow $(PRODUCT_NAME) to access your device motion"
Only for:
iOS

A string to set the NSMotionUsageDescription permission message.

Are you using this library in a bare React Native app?

Learn how to configure the native projects in the installation instructions in the expo-sensors repository.

API

import { DeviceMotion } from 'expo-sensors';

Constants

Gravity

Type: number


Constant value representing standard gravitational acceleration for Earth (9.80665 m/s^2).

Classes

DeviceMotion

Type: Class extends DeviceSensor<DeviceMotionMeasurement>

A base class for subscribable sensors. The events emitted by this class are measurements specified by the parameter type Measurement.

DeviceMotion Properties

Gravity

Type: number • Default: ExponentDeviceMotion.Gravity

Constant value representing standard gravitational acceleration for Earth (9.80665 m/s^2).

DeviceMotion Methods

addListener(listener)

NameTypeDescription
listenerListener<DeviceMotionMeasurement>

A callback that is invoked when a device motion sensor update is available. When invoked, the listener is provided a single argument that is a DeviceMotionMeasurement object.


Subscribe for updates to the device motion sensor.

Returns:

Subscription

A subscription that you can call remove() on when you would like to unsubscribe the listener.

getListenerCount()

Returns the registered listeners count.

Returns:

number

getPermissionsAsync()

Checks user's permissions for accessing sensor.

hasListeners()

Returns boolean which signifies if sensor has any listeners registered.

Returns:

boolean

isAvailableAsync()

You should always check the sensor availability before attempting to use it.

Returns whether the accelerometer is enabled on the device.

On mobile web, you must first invoke DeviceMotion.requestPermissionsAsync() in a user interaction (i.e. touch event) before you can use this module. If the status is not equal to granted then you should inform the end user that they may have to open settings.

On web this starts a timer and waits to see if an event is fired. This should predict if the iOS device has the device orientation API disabled in Settings > Safari > Motion & Orientation Access. Some devices will also not fire if the site isn't hosted with HTTPS as DeviceMotion is now considered a secure API. There is no formal API for detecting the status of DeviceMotion so this API can sometimes be unreliable on web.

Returns:

Promise<boolean>

A promise that resolves to a boolean denoting the availability of device motion sensor.

removeAllListeners()

Removes all registered listeners.

Returns:

void

removeSubscription(subscription)

NameTypeDescription
subscriptionSubscription

A subscription to remove.


Removes the given subscription.

Returns:

void

requestPermissionsAsync()

Asks the user to grant permissions for accessing sensor.

setUpdateInterval(intervalMs)

NameTypeDescription
intervalMsnumber

Desired interval in milliseconds between sensor updates.

Starting from Android 12 (API level 31), the system has a 200ms limit for each sensor updates.

If you need an update interval less than 200ms, you should:

  • add android.permission.HIGH_SAMPLING_RATE_SENSORS to app.json permissions field
  • or if you are using bare workflow, add <uses-permission android:name="android.permission.HIGH_SAMPLING_RATE_SENSORS"/> to AndroidManifest.xml.

Set the sensor update interval.

Returns:

void

Interfaces

PermissionResponse

An object obtained by permissions get and request functions.

PermissionResponse Properties

NameTypeDescription
canAskAgainboolean

Indicates if user can be asked again for specific permission. If not, one should be directed to the Settings app in order to enable/disable the permission.

expiresPermissionExpiration

Determines time when the permission expires.

grantedboolean

A convenience boolean that indicates if the permission is granted.

statusPermissionStatus

Determines the status of the permission.


Types

DeviceMotionMeasurement

NameTypeDescription
accelerationnull | { x: number, y: number, z: number }

Device acceleration on the three axis as an object with x, y, z keys. Expressed in meters per second squared (m/s^2).

accelerationIncludingGravity{ x: number, y: number, z: number }

Device acceleration with the effect of gravity on the three axis as an object with x, y, z keys. Expressed in meters per second squared (m/s^2).

intervalnumber

Interval at which data is obtained from the native platform. Expressed in milliseconds (ms).

orientationDeviceMotionOrientation

Device orientation based on screen rotation. Value is one of:

  • 0 (portrait),
  • 90 (right landscape),
  • 180 (upside down),
  • -90 (left landscape).
rotation{ alpha: number, beta: number, gamma: number }

Device's orientation in space as an object with alpha, beta, gamma keys where alpha is for rotation around Z axis, beta for X axis rotation and gamma for Y axis rotation.

rotationRatenull | { alpha: number, beta: number, gamma: number }

Device's rate of rotation in space expressed in degrees per second (deg/s).

PermissionExpiration

Literal Type: multiple types

Permission expiration time. Currently, all permissions are granted permanently.

Acceptable values are: 'never' | number

Subscription

NameTypeDescription
remove() => void

A method to unsubscribe the listener.

Enums

DeviceMotionOrientation

DeviceMotionOrientation Values

LeftLandscape

DeviceMotionOrientation.LeftLandscape = -90

Portrait

DeviceMotionOrientation.Portrait = 0

RightLandscape

DeviceMotionOrientation.RightLandscape = 90

UpsideDown

DeviceMotionOrientation.UpsideDown = 180

PermissionStatus

PermissionStatus Values

DENIED

PermissionStatus.DENIED = "denied"

User has denied the permission.

GRANTED

PermissionStatus.GRANTED = "granted"

User has granted the permission.

UNDETERMINED

PermissionStatus.UNDETERMINED = "undetermined"

User hasn't granted or denied the permission yet.

Permissions

iOS

The following usage description keys are used by this library:

Info.plist KeyDescription

NSMotionUsageDescription

A message that tells the user why the app is requesting access to the device’s motion data.