---
title: Magnetometer
description: A library that provides access to the device's magnetometer sensor.
sourceCodeUrl: 'https://github.com/expo/expo/tree/sdk-57/packages/expo-sensors'
packageName: 'expo-sensors'
iconUrl: '/static/images/packages/expo-sensors.png'
platforms: ['android', 'ios', 'expo-go']
---

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# Expo Magnetometer

A library that provides access to the device's magnetometer sensor.
Android, iOS, Included in Expo Go

`Magnetometer` from `expo-sensors` provides access to the device magnetometer sensor(s) to respond to and measure the changes in the magnetic field measured in microtesla (`μT`).

You can access the calibrated values with `Magnetometer` and uncalibrated raw values with `MagnetometerUncalibrated`.

## Installation

```sh
# npm
npx expo install expo-sensors

# yarn
yarn expo install expo-sensors

# pnpm
pnpm expo install expo-sensors

# bun
bun expo install expo-sensors
```

If you are installing this in an [existing React Native app](/bare/overview.md), make sure to [install `expo`](/bare/installing-expo-modules.md) in your project.

## Usage

```jsx
import { useState, useEffect } from 'react';
import { StyleSheet, Text, TouchableOpacity, View } from 'react-native';
import { Magnetometer } from 'expo-sensors';

export default function Compass() {
  const [{ x, y, z }, setData] = useState({
    x: 0,
    y: 0,
    z: 0,
  });
  const [subscription, setSubscription] = useState(null);

  const _slow = () => Magnetometer.setUpdateInterval(1000);
  const _fast = () => Magnetometer.setUpdateInterval(16);

  const _subscribe = () => {
    setSubscription(
      Magnetometer.addListener(result => {
        setData(result);
      })
    );
  };

  const _unsubscribe = () => {
    subscription && subscription.remove();
    setSubscription(null);
  };

  useEffect(() => {
    _subscribe();
    return () => _unsubscribe();
  }, []);

  return (
    <View style={styles.container}>
      <Text style={styles.text}>Magnetometer:</Text>
      <Text style={styles.text}>x: {x}</Text>
      <Text style={styles.text}>y: {y}</Text>
      <Text style={styles.text}>z: {z}</Text>
      <View style={styles.buttonContainer}>
        <TouchableOpacity onPress={subscription ? _unsubscribe : _subscribe} style={styles.button}>
          <Text>{subscription ? 'On' : 'Off'}</Text>
        </TouchableOpacity>
        <TouchableOpacity onPress={_slow} style={[styles.button, styles.middleButton]}>
          <Text>Slow</Text>
        </TouchableOpacity>
        <TouchableOpacity onPress={_fast} style={styles.button}>
          <Text>Fast</Text>
        </TouchableOpacity>
      </View>
    </View>
  );
}

const styles = StyleSheet.create({
  container: {
    flex: 1,
    justifyContent: 'center',
    paddingHorizontal: 10,
  },
  text: {
    textAlign: 'center',
  },
  buttonContainer: {
    flexDirection: 'row',
    alignItems: 'stretch',
    marginTop: 15,
  },
  button: {
    flex: 1,
    justifyContent: 'center',
    alignItems: 'center',
    backgroundColor: '#eee',
    padding: 10,
  },
  middleButton: {
    borderLeftWidth: 1,
    borderRightWidth: 1,
    borderColor: '#ccc',
  },
});
```

## API

```js
import { Magnetometer, MagnetometerUncalibrated } from 'expo-sensors';
```

## Classes

### `Magnetometer`

Supported platforms: Android, iOS.

Type: Class extends [DeviceSensor](/versions/latest/sdk/sensors.md)<[MagnetometerMeasurement](#magnetometermeasurement)\>

Magnetometer Methods

### `addListener(listener)`

Supported platforms: Android, iOS.

| Parameter | Type | Description |
| --- | --- | --- |
| `listener` | Listener<[MagnetometerMeasurement](#magnetometermeasurement)\> | A callback that is invoked when a magnetometer update is available. When invoked, the listener is provided with a single argument that is `MagnetometerMeasurement`. |

  

Subscribe for updates to the magnetometer.

Returns: `EventSubscription`

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

### `getListenerCount()`

Supported platforms: Android, iOS.

Returns the registered listeners count.

Returns: `number`

### `getPermissionsAsync()`

Supported platforms: Android, iOS.

Checks user's permissions for accessing sensor.

Returns: `Promise<permissionresponse>`

### `hasListeners()`

Supported platforms: Android, iOS.

Returns boolean which signifies if sensor has any listeners registered.

Returns: `boolean`

### `isAvailableAsync()`

Supported platforms: Android, iOS.

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

Check the availability of the device magnetometer. Requires at least Android 2.3 (API Level 9) and iOS 8.

Returns: `Promise<boolean>`

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

### `removeAllListeners()`

Supported platforms: Android, iOS.

Removes all registered listeners.

Returns: `void`

> **Deprecated:** use subscription.remove() instead.

### `removeSubscription(subscription)`

Supported platforms: Android, iOS.

| Parameter | Type |
| --- | --- |
| `subscription` | `EventSubscription` |

  

Returns: `void`

### `requestPermissionsAsync()`

Supported platforms: Android, iOS.

Asks the user to grant permissions for accessing sensor.

Returns: `Promise<permissionresponse>`

### `setUpdateInterval(intervalMs)`

Supported platforms: Android, iOS.

| Parameter | Type | Description |
| --- | --- | --- |
| `intervalMs` | `number` | Desired interval in milliseconds between sensor updates. Starting from Android 12 (API level 31), the system has a 200Hz limit for each sensor updates. |

  

Set the sensor update interval.

Returns: `void`

## Interfaces

### `Subscription`

Supported platforms: Android, iOS.

A subscription object that allows to conveniently remove an event listener from the emitter.

Subscription Methods

### `remove()`

Supported platforms: Android, iOS.

Removes an event listener for which the subscription has been created. After calling this function, the listener will no longer receive any events from the emitter.

Returns: `void`

## Types

### `MagnetometerMeasurement`

Supported platforms: Android, iOS.

Each of these keys represents the strength of magnetic field along that particular axis measured in microteslas (`μT`).

| Property | Type | Description |
| --- | --- | --- |
| timestamp | `number` | Timestamp of the measurement in seconds. |
| x | `number` | Value representing strength of magnetic field recorded in X axis. |
| y | `number` | Value representing strength of magnetic field recorded in Y axis. |
| z | `number` | Value representing strength of magnetic field recorded in Z axis. |

### `PermissionExpiration`

Supported platforms: Android, iOS.

Literal type: `union`

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

Acceptable values are: `'never'` | `number`

### `PermissionResponse`

Supported platforms: Android, iOS.

An object obtained by permissions get and request functions.

| Property | Type | Description |
| --- | --- | --- |
| canAskAgain | `boolean` | 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. |
| expires | `PermissionExpiration` | Determines time when the permission expires. |
| granted | `boolean` | A convenience boolean that indicates if the permission is granted. |
| status | [PermissionStatus](/versions/latest/sdk/expo.md#permissionstatus) | Determines the status of the permission. |

## Enums

### `PermissionStatus`

Supported platforms: Android, iOS.

#### `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.