AudioAccessoryKit

Automatic audio switching and intelligent audio routing for third-party audio accessories. Enables companion apps to register audio accessories with the system, report device placement, and declare capabilities so the system can seamlessly switch audio output. Available iOS 26.4+ / Swift 6.3.

Beta-sensitive. AudioAccessoryKit is new in iOS 26.4 and may change before GM. Re-check current Apple documentation before relying on specific API details.

AudioAccessoryKit builds on top of AccessorySetupKit. The accessory must first be paired via AccessorySetupKit before it can be registered for audio features. The central type is

AccessoryControlDevice

Contents

• Setup
• Session Management
• Audio Switching
• Device Placement
• Connected Audio Sources
• Feature Discovery
• Error Handling
• Common Mistakes
• Review Checklist
• References

Setup

Prerequisites

1. Pair the accessory over Bluetooth using AccessorySetupKit. This yields an

   ASAccessory

   object.
2. Import both frameworks in the companion app:

import AccessorySetupKit
import AudioAccessoryKit

Framework Availability

Session Management

Registering an Accessory

After pairing via AccessorySetupKit, register the accessory with

AccessoryControlDevice

let accessory: ASAccessory  // Obtained from AccessorySetupKit pairing

let capabilities: AccessoryControlDevice.Capabilities = [.audioSwitching, .placement]
try await AccessoryControlDevice.register(accessory, capabilities)

Registration activates the specified capabilities and tells the system to begin routing audio to the accessory.

Retrieving the Current Configuration

Access the device's current configuration at any time using the static

current(for:)

let device = try AccessoryControlDevice.current(for: accessory)
let currentConfig = device.configuration

This returns the

AccessoryControlDevice

ASAccessory

accessory

configuration

Updating Configuration

Push configuration changes to the system with

update(_:)

let device = try AccessoryControlDevice.current(for: accessory)
var config = device.configuration

config.devicePlacement = .onHead
try await device.update(config)

The update call is async and can throw

AccessoryControlDevice.Error

Audio Switching

Automatic audio switching lets the system intelligently route audio output to the correct device based on placement and connected sources.

Enabling Audio Switching

Declare the

.audioSwitching

let capabilities: AccessoryControlDevice.Capabilities = [.audioSwitching]
try await AccessoryControlDevice.register(accessory, capabilities)

For full automatic switching (including placement-based routing), include both capabilities:

let capabilities: AccessoryControlDevice.Capabilities = [.audioSwitching, .placement]
try await AccessoryControlDevice.register(accessory, capabilities)

Capabilities

AccessoryControlDevice.Capabilities

.audioSwitching

.placement

Both capabilities can be combined. Audio switching works without placement, but providing placement enables more intelligent routing decisions.

Device Placement

Report the physical position of the accessory to help the system make routing decisions. Update placement whenever the accessory detects a position change.

Placement Values

AccessoryControlDevice.Placement

.inEar

.onHead

.overTheEar

.offHead

Updating Placement

let device = try AccessoryControlDevice.current(for: accessory)
var config = device.configuration

config.devicePlacement = .inEar
try await device.update(config)

Common transitions:

• .offHead

  to

  .onHead

  or

  .inEar

  when the user puts on the accessory

• .onHead

  or

  .inEar

  to

  .offHead

  when removed
• Update promptly on every detected change for responsive audio routing

Connected Audio Sources

For accessories that connect to multiple Bluetooth devices simultaneously, inform the system which devices are connected. This lets the system route audio from the appropriate source.

Setting Audio Source Identifiers

Provide the Bluetooth address of connected devices as

Data

let device = try AccessoryControlDevice.current(for: accessory)
var config = device.configuration

let primaryBTAddress = Data([0x12, 0x34, 0x56, 0x78, 0x9A, 0xBC])
config.primaryAudioSourceDeviceIdentifier = primaryBTAddress

let secondaryBTAddress = Data([0xAB, 0xCD, 0xEF, 0x01, 0x23, 0x45])
config.secondaryAudioSourceDeviceIdentifier = secondaryBTAddress

try await device.update(config)

Update these identifiers when the Bluetooth connection state changes (new device connects, existing device disconnects).

Configuration Properties

AccessoryControlDevice.Configuration

deviceCapabilities

Capabilities

devicePlacement

Placement?

primaryAudioSourceDeviceIdentifier

Data?

secondaryAudioSourceDeviceIdentifier

Data?

Feature Discovery

Querying Capabilities

After registration, inspect the device's declared capabilities through its configuration:

let device = try AccessoryControlDevice.current(for: accessory)
let caps = device.configuration.deviceCapabilities

if caps.contains(.audioSwitching) {
    // Device supports automatic audio switching
}

if caps.contains(.placement) {
    // Device reports physical placement
}

Checking Placement

Read the current placement to determine if the accessory is being worn:

let device = try AccessoryControlDevice.current(for: accessory)

if let placement = device.configuration.devicePlacement {
    switch placement {
    case .inEar, .onHead, .overTheEar:
        // Accessory is being worn
        break
    case .offHead:
        // Accessory is not being worn
        break
    @unknown default:
        break
    }
}

Error Handling

AccessoryControlDevice.Error

.accessoryNotCapable

.invalidRequest

.invalidated

.unknown

Handle errors from registration and update calls:

do {
    try await AccessoryControlDevice.register(accessory, capabilities)
} catch let error as AccessoryControlDevice.Error {
    switch error {
    case .accessoryNotCapable:
        // Accessory hardware does not support requested capabilities
        break
    case .invalidRequest:
        // Check registration parameters
        break
    case .invalidated:
        // Re-register the device
        break
    case .unknown:
        // Log and retry
        break
    @unknown default:
        break
    }
}

Common Mistakes

DON'T: Register before pairing with AccessorySetupKit

// WRONG -- accessory not yet paired
let rawAccessory = ASAccessory()
try await AccessoryControlDevice.register(rawAccessory, [.audioSwitching])

// CORRECT -- use the ASAccessory from a completed pairing session
session.activate(on: .main) { event in
    if event.eventType == .accessoryAdded, let accessory = event.accessory {
        Task {
            try await AccessoryControlDevice.register(accessory, [.audioSwitching])
        }
    }
}

DON'T: Declare placement capability without updating placement

// WRONG -- registers placement but never updates it
try await AccessoryControlDevice.register(accessory, [.audioSwitching, .placement])
// System never receives placement data, reducing switching accuracy

// CORRECT -- update placement promptly after registration
try await AccessoryControlDevice.register(accessory, [.audioSwitching, .placement])
let device = try AccessoryControlDevice.current(for: accessory)
var config = device.configuration
config.devicePlacement = .offHead
try await device.update(config)

DON'T: Ignore connection state changes for multi-device accessories

// WRONG -- set audio source identifiers once and never update
config.primaryAudioSourceDeviceIdentifier = someAddress
try await device.update(config)
// Device disconnects, but system still thinks it's the primary source

// CORRECT -- update identifiers when connections change
func onDeviceDisconnected() {
    var config = device.configuration
    config.primaryAudioSourceDeviceIdentifier = nil
    Task { try await device.update(config) }
}

DON'T: Forget to handle the invalidated error

// WRONG -- ignores invalidation, keeps using stale device reference
try await device.update(config)  // Throws .invalidated, unhandled

// CORRECT -- catch invalidation and re-register
do {
    try await device.update(config)
} catch AccessoryControlDevice.Error.invalidated {
    try await AccessoryControlDevice.register(accessory, capabilities)
}

Review Checklist

• Accessory paired via AccessorySetupKit before AudioAccessoryKit registration
• Both

  AccessorySetupKit

  and

  AudioAccessoryKit

  imported
• Capabilities declared at registration match actual hardware support

• .placement

  capability accompanied by ongoing placement updates
• Placement transitions (on/off head) reported promptly
• Audio source device identifiers updated on Bluetooth connection changes
• All

  AccessoryControlDevice.Error

  cases handled, including

  @unknown default

• update(_:)

  calls use

  try await

  and handle errors
• Invalidated device references re-registered when needed
• Deployment target set to iOS 26.4+ or iPadOS 26.4+

References

• Extended patterns (registration flow, placement monitoring, multi-device coordination): references/audioaccessorykit-patterns.md
• AudioAccessoryKit framework
• Supporting automatic audio switching
• AccessoryControlDevice
• AccessoryControlDevice.Configuration
• AccessoryControlDevice.Capabilities
• AccessoryControlDevice.Placement
• AccessorySetupKit framework (prerequisite for pairing)