Working with Sensors

1. Using Accelerometer

Property	Description	Values
acceleration.x	X-axis acceleration in m/s²	`number`
acceleration.y	Y-axis acceleration in m/s²	`number`
acceleration.z	Z-axis acceleration in m/s²	`number`
gravity.x	X-axis gravity in m/s²	`number`
gravity.y	Y-axis gravity in m/s²	`number`
gravity.z	Z-axis gravity in m/s²	`number`
userAcceleration.x	X-axis user acceleration in m/s²	`number`
userAcceleration.y	Y-axis user acceleration in m/s²	`number`
userAcceleration.z	Z-axis user acceleration in m/s²	`number`

Example: Reading Accelerometer Data

import { Accelerometer } from 'expo-sensors';

const subscribe = Accelerometer.addListener((accelerometerData) => {
  console.log("Acceleration: ", accelerometerData.acceleration);
});

// Unsubscribe when done
// subscribe.remove();

Note: Ensure that the device has accelerometer hardware and permissions are granted for sensor access.

2. Using Gyroscope

Property	Description	Values
Gyroscope.isAvailable	Indicates if gyroscope sensor is available	`true` or `false`
Gyroscope.addListener	Registers a listener for gyroscope data	Function callback
Gyroscope.removeListeners	Removes all gyroscope listeners	None

Gyroscope.addListener((gyroData) => {
  console.log("Gyroscope Data:", gyroData);
});

Example: Stop Listening to Gyroscope

Gyroscope.removeListeners();

Note: On some devices, gyroscope data might not be available or may require additional permissions.

3. Using Magnetometer

Property	Description	Values
magnetometer	Provides access to the device's magnetometer sensor data	`true` or `false`

Example: Reading Magnetometer Data

import { Magnetometer } from 'expo-sensors';

Magnetometer.addListener((magnetometerData) => {
  console.log('Magnetic field (microtesla):', magnetometerData);
});

// Start listening
Magnetometer.setUpdateInterval(100); // Update every 100ms

Note: The magnetometer sensor provides data in microtesla (µT) units.

Warning: Not all devices support magnetometer sensors. Always check for sensor availability before using.

Field	Description	Unit
x	X-axis magnetic field strength	µT
y	Y-axis magnetic field strength	µT
z	Z-axis magnetic field strength	µT

4. Using Barometer

Property	Description	Values
barometer.pressure	Current atmospheric pressure in hectopascals (hPa)	`1013.25`
barometer.altitude	Estimated altitude in meters based on pressure	`0`

Example: Reading Barometer Data

import { Barometer } from &#x27;expo-sensors&#x27;;

Barometer.addListener((data) => {
  console.log("Pressure:", data.pressure);
  console.log("Altitude:", data.altitude);
});

Barometer.setUpdateInterval(1000); // Update every second

Note: Barometer sensor data is only available on devices with a pressure sensor.

Warning: Altitude calculation is approximate and may vary due to local weather conditions.

5. Using Pedometer

Property	Description	Values
isAvailable	Indicates if the pedometer sensor is available on the device	`true` or `false`
stepCount	Current step count since the sensor started tracking	`number`
lastUpdate	Timestamp of the last update from the sensor	`Date`

Example: Reading Pedometer Data

import * as Expo from 'expo-sensors';<br><br>// Check if pedometer is available<br>const isAvailable = await Expo.Pedometer.isAvailableAsync();<br><br>// Start watching pedometer data<br>const { steps, lastUpdate } = await Expo.Pedometer.watchPedometerDataAsync(<br>  (data) => {<br>    console.log('Steps:', data.steps);<br>    console.log('Last Update:', data.lastUpdate);<br>  }<br>);

Note: The pedometer sensor is only available on devices with a step counter (e.g., iOS devices with CoreMotion support).

6. Setting Update Interval

Property	Values	Description
interval	`100` ms (default)	Update interval in milliseconds
fastestInterval	`0` ms (default)	Fastest update interval allowed

Example: Configure Update Interval

import { Accelerometer } from 'expo-sensors';

Accelerometer.setUpdateInterval(200); // Update every 200ms

Note: Setting a faster interval may impact battery life and performance.

7. Adding Sensor Listeners

Example: Adding a Sensor Listener

import { Sensor } from 'expo-sensors';

const sensorListener = Sensor.watchSensor(
  Sensor.TYPE_ACCELEROMETER,
  (accelerometerData) => {
    console.log("Acceleration X:", accelerometerData.x);
    console.log("Acceleration Y:", accelerometerData.y);
    console.log("Acceleration Z:", accelerometerData.z);
  },
  100 // Update interval in milliseconds
);

// To stop listening:
// Sensor.clearSensorListener(sensorListener);

Parameter	Type	Description
sensorType	`string`	Type of sensor to listen to (e.g., `TYPE_ACCELEROMETER`)
listener	`function`	Callback function that receives sensor data
interval	`number`	Update interval in milliseconds (optional)

Note: The sensor listener will continue running until explicitly cleared using Sensor.clearSensorListener().

8. Removing Listeners

Example: Removing a Sensor Listener

import { Sensor } from 'expo-sensors';

// Assume we have a listener set up
const sensorListener = Sensor.addListener(
  Sensor.SensorType.ACCELEROMETER,
  (data) => {
    console.log('Accelerometer data:', data);
  }
);

// Remove the listener
Sensor.removeListener(sensorListener);

Method	Description	Parameters
Sensor.removeListener()	Removes a previously added sensor listener	`listener` - The listener to remove

Note: Always remove listeners when they are no longer needed to prevent memory leaks and unnecessary updates.

9. Using Device Motion

Property	Description	Values	Notes
acceleration	Current acceleration along the x, y, and z axes	`{ x: number, y: number, z: number }`	Unit is in `m/s²`
accelerationIncludingGravity	Acceleration including gravity	`{ x: number, y: number, z: number }`	Unit is in `m/s²`
rotationRate	Rotation rate around the x, y, and z axes	`{ alpha: number, beta: number, gamma: number }`	Unit is in `deg/s`
interval	Interval in milliseconds between updates	`number`	Default is `100` ms

Example: Using Device Motion

import { DeviceMotion } from 'expo-sensors';

const subscribe = DeviceMotion.addListener((motionData) => {
  console.log('Acceleration:', motionData.acceleration);
  console.log('Rotation Rate:', motionData.rotationRate);
});

// Start listening
DeviceMotion.setUpdateInterval(100);

// Stop listening
// DeviceMotion.removeSubscription(subscribe);

Note: On some devices, accelerationIncludingGravity may not be available.

10. Checking Sensor Availability

Sensor	Availability	Notes
Accelerometer	Available	Supported on all platforms
Gyroscope	Available	Supported on all platforms
Magnetometer	Available	Supported on all platforms
Barometer	Available	Only available on devices with barometer hardware
AmbientLight	Available	Supported on all platforms

Example: Check Sensor Availability

import { Accelerometer, Gyroscope } from 'expo-sensors';

const isAccelerometerAvailable = await Accelerometer.isAvailableAsync();
const isGyroscopeAvailable = await Gyroscope.isAvailableAsync();

console.log('Accelerometer available:', isAccelerometerAvailable);
console.log('Gyroscope available:', isGyroscopeAvailable);

11. Handling Sensor Errors

Example: Error Handling with Sensor Data

import { Sensor } from 'expo-sensors';

try {
  const data = await Sensor.getSensorDataAsync(Sensor.Type.ACCELEROMETER);
  console.log('Sensor data:', data);
} catch (error) {
  console.error('Sensor error:', error.message);
  // Handle specific sensor errors
  if (error.code === 'SENSOR_NOT_AVAILABLE') {
    console.warn('Sensor not available on this device');
  }
}

Error Code	Description	Handling Recommendation
SENSOR_NOT_AVAILABLE	Sensor hardware not present or disabled	Check device capabilities and provide fallback UI
SENSOR_PERMISSION_DENIED	User denied sensor access permission	Prompt user to enable permissions in settings
SENSOR_DATA_ERROR	Malformed or corrupted sensor data	Retry read operation or log error for debugging

Note: Always wrap sensor operations in try-catch blocks to gracefully handle runtime errors.

Warning: Some sensors may return null or invalid data when the device is in low-power mode.

12. Using Light Sensor

Property	Description	Values
ambientLight	Current ambient light level in lux	`number`

Example: Reading Light Sensor Data

import { Sensor } from 'expo-sensors';

const subscribe = Sensor.watchSensor(
  Sensor.TYPE_LIGHT,
  (data) => {
    console.log('Light level:', data.ambientLight);
  }
);

// Unsubscribe when done
// subscribe.remove();

Note: The light sensor may not be available on all devices.

Warning: Continuous sensor reading can drain battery quickly.