Google Home Device Integration in Mobile IoT App

Google Home Device Integration into Mobile IoT App

Google Home SDK became publicly available in 2023 after years of closed beta. Before that only path — Google Home API via REST, limiting control and requiring OAuth per user via Google account. Now two paths: Google Home SDK for Android (native integration) and Device Access API (REST/gRPC, works with Android and iOS).

Device Access API: REST Integration for iOS and Flutter

Device Access works with Nest devices (thermostats, cameras, doorbell cameras). Authorization via OAuth 2.0, after which app gets access to Structures, Rooms and Devices:

GET https://smartdevicemanagement.googleapis.com/v1/enterprises/{projectId}/devices
Authorization: Bearer {access_token}

Response contains device list with traits. Nest Learning 3rd gen thermostat returns:

{
  "name": "enterprises/project-id/devices/device-id",
  "type": "sdm.devices.types.THERMOSTAT",
  "traits": {
    "sdm.devices.traits.ThermostatMode": {
      "mode": "HEAT",
      "availableModes": ["HEAT", "COOL", "HEATCOOL", "OFF"]
    },
    "sdm.devices.traits.ThermostatTemperatureSetpoint": {
      "heatCelsius": 21.5
    },
    "sdm.devices.traits.Temperature": {
      "ambientTemperatureCelsius": 19.8
    }
  }
}

Control — via ExecuteCommand:

// iOS, Alamofire
func setThermostatMode(_ mode: String, deviceName: String) async throws {
    let url = "https://smartdevicemanagement.googleapis.com/v1/\(deviceName):executeCommand"
    let body: [String: Any] = [
        "command": "sdm.devices.commands.ThermostatMode.SetMode",
        "params": ["mode": mode]
    ]
    _ = try await AF.request(url, method: .post, parameters: body,
                              encoding: JSONEncoding.default,
                              headers: authHeaders)
        .serializingDecodable(CommandResponse.self)
        .value
}

Authorization via Google Sign-In SDK with scope https://www.googleapis.com/auth/sdm.service. Store refresh token in Keychain — DeviceAccess tokens live 1 hour.

Android: Google Home SDK

Android Google Home SDK provides native ecosystem access, including Matter devices:

// build.gradle.kts
implementation("com.google.home:google-home-sdk:1.1.0")

Initialization:

val homeClient = HomeManager.getHomeClient(context)

homeClient.getHomes()
    .flowOn(Dispatchers.IO)
    .collect { homes ->
        homes.forEach { home ->
            home.devices().collect { devices ->
                devices.forEach { device ->
                    processDevice(device)
                }
            }
        }
    }

Interesting SDK feature — reactive model based on Kotlin Flow. Device state is Flow, automatically emits new values on change:

suspend fun observeThermostat(device: HomeDevice) {
    device.trait(ThermostatMode)
        ?.changes()
        ?.collect { mode ->
            updateUI(mode.mode)
        }
}

Execute commands via same trait objects:

val thermostatTrait = device.trait(ThermostatMode) ?: return
thermostatTrait.setMode(ThermostatMode.Mode.COOL)

Nest Cameras: WebRTC Streaming

Camera Access trait returns rtspUrl or WebRTC offer, depending on camera model. New Nest Cam (2021+) work only via WebRTC:

val cameraLiveStream = device.trait(CameraLiveStream)
val streamResponse = cameraLiveStream?.generateWebRtcStream(
    offerSdp = localPeerConnection.localDescription?.description ?: ""
)
// Pass streamResponse.answerSdp to RTCPeerConnection
peerConnection.setRemoteDescription(
    RTCSessionDescription(RTCSessionDescription.Type.ANSWER, streamResponse.answerSdp)
)

Common mistake: don't update stream token. WebRTC session lives 5 minutes, then Nest closes connection. Need background timer calling extendWebRtcStream() 30 seconds before expiry.

Ecosystem Limitations

Device Access API requires Google approval for each project — submit request via console, response 1-5 business days. Fee: $5 project registration. Cameras don't work in Device Access without Nest Aware subscription on user account — must explicitly mention in UX.

Google Home SDK Android still Developer Preview in 2024, API may change. For production solutions with cameras, Device Access API more reliable.

Integration timeline: Device Access API for iOS — 2-3 weeks; Android Google Home SDK with Matter — 3-4 weeks; Flutter with both — 5-6 weeks. Cost calculated individually after analyzing requirements.