Sensorkit

Overview and Requirements

SensorKit enables research apps to record and fetch sensor data across iPhone and Apple Watch. The framework requires:

1. Apple-approved research study -- submit a proposal at researchandcare.org.
2. SensorKit entitlement -- Apple grants com.apple.developer.sensorkit.reader.allow only for approved studies.
3. Manual provisioning profile -- Xcode requires an explicit App ID with the SensorKit capability enabled.
4. User authorization -- the system presents a Research Sensor & Usage Data sheet that users approve per-sensor.
5. 24-hour data hold -- newly recorded data is inaccessible for 24 hours, giving users time to delete data they do not want to share.

An app can access up to 7 days of prior recorded data for an active sensor.

Entitlements

Add the SensorKit reader entitlement to a .entitlements file. List only the sensors your study uses:

<key>com.apple.developer.sensorkit.reader.allow</key>
<array>
    <string>ambient-light-sensor</string>
    <string>motion-accelerometer</string>
    <string>motion-rotation-rate</string>
    <string>device-usage</string>
    <string>keyboard-metrics</string>
    <string>messages-usage</string>
    <string>phone-usage</string>
    <string>visits</string>
    <string>pedometer</string>
    <string>on-wrist</string>
</array>

Xcode build settings for manual signing:

Info.plist Configuration

Three keys are required:

<!-- Study purpose shown in the authorization sheet -->
<key>NSSensorKitUsageDescription</key>
<string>This study monitors activity patterns for sleep research.</string>

<!-- Link to your study's privacy policy -->
<key>NSSensorKitPrivacyPolicyURL</key>
<string>https://example.com/privacy-policy</string>

<!-- Per-sensor usage explanations -->
<key>NSSensorKitUsageDetail</key>
<dict>
    <key>SRSensorUsageMotion</key>
    <dict>
        <key>Description</key>
        <string>Measures physical activity levels during the study.</string>
        <key>Required</key>
        <true/>
    </dict>
    <key>SRSensorUsageAmbientLightSensor</key>
    <dict>
        <key>Description</key>
        <string>Records ambient light to assess sleep environment.</string>
    </dict>
</dict>

If Required is true and the user denies that sensor, the system warns them that the study needs it and offers a chance to reconsider.

Authorization

Request authorization for the sensors your study needs. The system shows the Research Sensor & Usage Data sheet on first request.

import SensorKit

let reader = SRSensorReader(sensor: .ambientLightSensor)

// Request authorization for multiple sensors at once
SRSensorReader.requestAuthorization(
    sensors: [.ambientLightSensor, .accelerometer, .keyboardMetrics]
) { error in
    if let error {
        print("Authorization request failed: \(error)")
    }
}

Check a reader's current status before recording:

switch reader.authorizationStatus {
case .authorized:
    reader.startRecording()
case .denied:
    // User declined -- direct to Settings > Privacy > Research Sensor & Usage Data
    break
case .notDetermined:
    // Request authorization first
    break
@unknown default:
    break
}

Monitor status changes through the delegate:

func sensorReader(_ reader: SRSensorReader, didChange authorizationStatus: SRAuthorizationStatus) {
    switch authorizationStatus {
    case .authorized:
        reader.startRecording()
    case .denied:
        reader.stopRecording()
    default:
        break
    }
}

Available Sensors

Device Sensors

App Activity Sensors

User Activity Sensors

Environment Sensors

SRSensorReader

SRSensorReader is the central class for accessing sensor data. Each instance reads from a single sensor.

import SensorKit

// Create a reader for one sensor
let lightReader = SRSensorReader(sensor: .ambientLightSensor)
let keyboardReader = SRSensorReader(sensor: .keyboardMetrics)

// Assign delegate to receive callbacks
lightReader.delegate = self
keyboardReader.delegate = self

The reader communicates entirely through SRSensorReaderDelegate:

Recording and Fetching Data

Start and Stop Recording

// Begin recording -- sensor stays active as long as any app has a stake
reader.startRecording()

// Stop recording -- framework deactivates the sensor when
// no app or system process is using it
reader.stopRecording()

Fetch Data

Build an SRFetchRequest with a time range and target device, then pass it to the reader:

let request = SRFetchRequest()
request.device = SRDevice.current
request.from = SRAbsoluteTime(CFAbsoluteTimeGetCurrent() - 86400 * 2)  // 2 days ago
request.to = SRAbsoluteTime.current()

reader.fetch(request)

Receive results through the delegate:

func sensorReader(
    _ reader: SRSensorReader,
    fetching request: SRFetchRequest,
    didFetchResult result: SRFetchResult<AnyObject>
) -> Bool {
    let timestamp = result.timestamp

    switch reader.sensor {
    case .ambientLightSensor:
        if let sample = result.sample as? SRAmbientLightSample {
            let lux = sample.lux
            let chromaticity = sample.chromaticity
            let placement = sample.placement
            processSample(lux: lux, chromaticity: chromaticity, at: timestamp)
        }
    case .keyboardMetrics:
        if let sample = result.sample as? SRKeyboardMetrics {
            let words = sample.totalWords
            let speed = sample.typingSpeed
            processKeyboard(words: words, speed: speed, at: timestamp)
        }
    case .deviceUsageReport:
        if let sample = result.sample as? SRDeviceUsageReport {
            let wakes = sample.totalScreenWakes
            let unlocks = sample.totalUnlocks
            processUsage(wakes: wakes, unlocks: unlocks, at: timestamp)
        }
    default:
        break
    }

    return true  // Return true to continue receiving results
}

func sensorReader(_ reader: SRSensorReader, didCompleteFetch request: SRFetchRequest) {
    print("Fetch complete for \(reader.sensor)")
}

func sensorReader(
    _ reader: SRSensorReader,
    fetching request: SRFetchRequest,
    failedWithError error: any Error
) {
    print("Fetch failed: \(error)")
}

Data Holding Period

SensorKit imposes a 24-hour holding period on newly recorded data. Fetch requests whose time range overlaps this period return no results. Design data collection workflows around this delay.

SRDevice

SRDevice identifies the hardware source for sensor samples. Use it to distinguish data from iPhone versus Apple Watch.

// Get the current device
let currentDevice = SRDevice.current
print("Model: \(currentDevice.model)")
print("System: \(currentDevice.systemName) \(currentDevice.systemVersion)")

// Fetch all available devices for a sensor
reader.fetchDevices()

Handle fetched devices through the delegate:

func sensorReader(_ reader: SRSensorReader, didFetch devices: [SRDevice]) {
    for device in devices {
        let request = SRFetchRequest()
        request.device = device
        request.from = SRAbsoluteTime(CFAbsoluteTimeGetCurrent() - 86400)
        request.to = SRAbsoluteTime.current()
        reader.fetch(request)
    }
}

func sensorReader(_ reader: SRSensorReader, fetchDevicesDidFailWithError error: any Error) {
    print("Failed to fetch devices: \(error)")
}

SRDevice Properties

Common Mistakes

DON'T: Attempt to use SensorKit without the entitlement

// WRONG -- fails at runtime with SRError.invalidEntitlement
let reader = SRSensorReader(sensor: .ambientLightSensor)
reader.startRecording()

// CORRECT -- obtain entitlement from Apple first, configure manual
// provisioning profile, then use SensorKit

DON'T: Expect immediate data access

// WRONG -- fetching data recorded moments ago returns nothing
reader.startRecording()
// ... record for a few minutes ...
let request = SRFetchRequest()
request.from = SRAbsoluteTime(CFAbsoluteTimeGetCurrent() - 300)
request.to = SRAbsoluteTime.current()
reader.fetch(request)  // Empty results due to 24-hour hold

// CORRECT -- fetch data that is at least 24 hours old
request.from = SRAbsoluteTime(CFAbsoluteTimeGetCurrent() - 86400 * 3)
request.to = SRAbsoluteTime(CFAbsoluteTimeGetCurrent() - 86400)
reader.fetch(request)

DON'T: Forget to set the delegate before fetching

// WRONG -- no delegate means no callbacks, results are silently lost
let reader = SRSensorReader(sensor: .accelerometer)
reader.startRecording()
reader.fetch(request)

// CORRECT -- assign delegate first
reader.delegate = self
reader.startRecording()
reader.fetch(request)

DON'T: Skip per-sensor Info.plist usage detail

// WRONG -- missing NSSensorKitUsageDetail for the sensor
// Authorization sheet shows no explanation, user is less likely to approve

// CORRECT -- add usage detail for every sensor you request
// See Info.plist Configuration section above

DON'T: Ignore SRError codes

// WRONG -- generic error handling
func sensorReader(_ reader: SRSensorReader, fetching: SRFetchRequest, failedWithError error: any Error) {
    print("Error")
}

// CORRECT -- handle specific error codes
func sensorReader(_ reader: SRSensorReader, fetching: SRFetchRequest, failedWithError error: any Error) {
    if let srError = error as? SRError {
        switch srError.code {
        case .invalidEntitlement:
            // Entitlement missing or sensor not in entitlement array
            break
        case .noAuthorization:
            // User has not authorized this sensor
            break
        case .dataInaccessible:
            // Data in 24-hour holding period or otherwise unavailable
            break
        case .fetchRequestInvalid:
            // Invalid time range or device
            break
        case .promptDeclined:
            // User declined the authorization prompt
            break
        @unknown default:
            break
        }
    }
}

Review Checklist

• Apple-approved research study in place before development
• com.apple.developer.sensorkit.reader.allow entitlement lists only needed sensors
• Manual provisioning profile with explicit App ID and SensorKit capability
• NSSensorKitUsageDescription in Info.plist with clear study purpose
• NSSensorKitPrivacyPolicyURL in Info.plist with valid privacy policy URL
• NSSensorKitUsageDetail entries for every requested sensor
• Required key set appropriately for essential vs. optional sensors
• Authorization requested before recording, status checked before fetching
• Delegate assigned before calling startRecording() or fetch(_:)
• Fetch request time ranges account for 24-hour data holding period
• SRError codes handled in all failure delegate methods
• fetchDevices() used to discover available devices before fetching
• stopRecording() called when data collection is complete
• sensorReader(_:fetching:didFetchResult:) returns true to continue or false to stop

References

• Extended patterns (delegate wiring, multi-sensor manager, sample type details): references/sensorkit-patterns.md
• SensorKit framework
• SRSensorReader
• SRSensor
• SRDevice
• SRFetchRequest
• Configuring your project for sensor reading
• com.apple.developer.sensorkit.reader.allow