EventManager

The EventManager handles event subscriptions and dispatching within a AppSession. It provides methods for subscribing to various event types from the MentraOS platform.

You access the EventManager through the events property of a AppSession instance:

const eventManager = appSession.events

Event Handler Methods

onTranscription()

Registers a handler for real-time speech transcription events.

onTranscription(handler: (data: TranscriptionData) => void): () => void

Parameters:

• handler: Callback function that receives TranscriptionData objects

Returns: An unsubscribe function to remove the handler

Example:

const unsubscribe = appSession.events.onTranscription(data => {
  console.log(`Transcription: ${data.text}, Final: ${data.isFinal}`)
  if (data.isFinal) {
    // Process the final transcription
  }
})

// Later, to stop receiving events:
unsubscribe()

onHeadPosition()

Registers a handler for head position change events.

onHeadPosition(handler: (data: HeadPosition) => void): () => void

Parameters:

• handler: Callback function that receives HeadPosition objects

Returns: An unsubscribe function to remove the handler

Example:

appSession.events.onHeadPosition(data => {
  if (data.position === "up") {
    console.log("User looked up")
  } else if (data.position === "down") {
    console.log("User looked down")
  }
})

onButtonPress()

Registers a handler for hardware button press events on the glasses.

onButtonPress(handler: (data: ButtonPress) => void): () => void

Parameters:

• handler: Callback function that receives ButtonPress objects

Returns: An unsubscribe function to remove the handler

Example:

appSession.events.onButtonPress(data => {
  console.log(`Button ${data.buttonId} was ${data.pressType} pressed`)
})

onPhoneNotifications()

Registers a handler for notifications received from the connected phone.

onPhoneNotifications(handler: (data: PhoneNotification) => void): () => void

Parameters:

• handler: Callback function that receives PhoneNotification objects

Returns: An unsubscribe function to remove the handler

Example:

appSession.events.onPhoneNotifications(data => {
  console.log(`Notification from ${data.app}: ${data.title} - ${data.content}`)
})

onGlassesBattery()

Registers a handler for glasses battery update events.

onGlassesBattery(handler: (data: GlassesBatteryUpdate) => void): () => void

Parameters:

• handler: Callback function that receives GlassesBatteryUpdate objects

Returns: An unsubscribe function to remove the handler

Example:

appSession.events.onGlassesBattery(data => {
  console.log(`Glasses battery: ${data.level}%, Charging: ${data.charging}`)
})

onPhoneBattery()

Registers a handler for phone battery update events.

onPhoneBattery(handler: (data: PhoneBatteryUpdate) => void): () => void

Parameters:

• handler: Callback function that receives PhoneBatteryUpdate objects

Returns: An unsubscribe function to remove the handler

onVoiceActivity()

Registers a handler for Voice Activity Detection (VAD) events.

onVoiceActivity(handler: (data: Vad) => void): () => void

Parameters:

• handler: Callback function that receives Vad objects

Returns: An unsubscribe function to remove the handler

Example:

appSession.events.onVoiceActivity(data => {
  if (data.status === true || data.status === "true") {
    console.log("User is speaking")
  } else {
    console.log("User stopped speaking")
  }
})

onLocation()

An event handler for raw location updates.

Use the LocationManager to access location data, as it provides a simple interface for both streaming and polling.

onLocation(handler: (data: LocationUpdate) => void): () => void

Parameters:

• handler: Callback function that receives LocationUpdate objects

Returns: An unsubscribe function to remove the handler

onCalendarEvent()

Registers a handler for calendar event notifications.

onCalendarEvent(handler: (data: CalendarEvent) => void): () => void

Parameters:

• handler: Callback function that receives CalendarEvent objects

Returns: An unsubscribe function to remove the handler

onAudioChunk()

Registers a handler for raw audio data chunks. Requires explicit subscription.

onAudioChunk(handler: (data: AudioChunk) => void): () => void

Parameters:

• handler: Callback function that receives AudioChunk objects

Returns: An unsubscribe function to remove the handler

Note: Audio chunks require an explicit subscription using appSession.subscribe(StreamType.AUDIO_CHUNK).

System Event Handlers

onConnected()

Registers a handler for when the WebSocket connection is successfully established and authenticated.

onConnected(handler: (data: AppSettings | undefined) => void): () => void

Parameters:

• handler: Callback function that receives optional AppSettings upon connection

Returns: An unsubscribe function to remove the handler

Example:

appSession.events.onConnected(settings => {
  console.log("Connected to MentraOS Cloud")
  if (settings) {
    console.log("Initial settings received:", settings)
  }
})

onDisconnected()

Registers a handler for when the WebSocket connection is closed or lost.

onDisconnected(handler: (reason: string) => void): () => void

Parameters:

• handler: Callback function that receives a reason string

Returns: An unsubscribe function to remove the handler

Example:

appSession.events.onDisconnected(reason => {
  console.log(`Disconnected from MentraOS Cloud. Reason: ${reason}`)
})

onError()

Registers a handler for WebSocket or SDK-level errors.

onError(handler: (error: WebSocketError | Error) => void): () => void

Parameters:

• handler: Callback function that receives a WebSocketError or standard Error object

Returns: An unsubscribe function to remove the handler

Example:

appSession.events.onError(error => {
  console.error("Error in App session:", error)
})

onSettingsUpdate()

Registers a handler for when the application settings are updated by the user via MentraOS Cloud.

onSettingsUpdate(handler: (settings: AppSettings) => void): () => void

Parameters:

• handler: Callback function that receives the complete updated AppSettings array

Returns: An unsubscribe function to remove the handler

Example:

appSession.events.onSettingsUpdate(settings => {
  console.log("Settings updated:", settings)
})

onSettingChange()

Registers a handler that triggers only when a specific setting's value changes.

onSettingChange<T>(
  key: string,
  handler: (value: T, previousValue: T | undefined) => void
): () => void

Parameters:

• key: The key of the setting to monitor
• handler: Callback function that receives the new value and the previous value (or undefined initially)

Returns: An unsubscribe function to remove the handler

Example:

appSession.events.onSettingChange<boolean>("enableNotifications", (newValue, oldValue) => {
  console.log(`enableNotifications changed from ${oldValue} to ${newValue}`)
  if (newValue) {
    // Enable notification features
  } else {
    // Disable notification features
  }
})

Generic Event Handler

on()

Generic event handler for any StreamType. Use specific methods above where possible.

on<T extends StreamType>(
  type: T,
  handler: (data: StreamDataTypes[T]) => void
): () => void

Parameters:

• type: The StreamType to listen for
• handler: Callback function that receives data of the appropriate type for the specified StreamType

Returns: An unsubscribe function to remove the handler

Example:

import {StreamType} from "@mentra/sdk"

// Subscribe to a specific stream type
appSession.events.on(StreamType.LOCATION_UPDATE, data => {
  console.log(`Location update: ${data.lat}, ${data.lng}`)
})

// Using a language-specific stream
const transcriptionStream = createTranscriptionStream("en-US")
appSession.events.on(transcriptionStream, data => {
  console.log(`English transcription: ${data.text}`)
})