Google Home Screen Control

Turn every monitor on your Windows 11 PC on and off by voice, through Google Home Mini over local Matter — while the computer keeps running.

OK Google, turn off Computer Screen
OK Google, turn on  Computer Screen

When you turn the screens off, Windows, the network, and background programs keep running — no sleep, no lock, no sign-out. Moving the mouse or pressing a key wakes the displays as usual.

Everything runs on your own machine and LAN. There is no cloud bridge, no VPS, no Home Assistant, and no inbound port opened to the internet.

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Contents

• Features
• How it works
• Requirements
• Installation
• First-time Matter pairing
• Voice control
• How it behaves
• Diagnostics
• Uninstall
• Security
• Design notes
• Project structure
• Contributing
• License

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Features

• One voice switch for all displays. Every connected monitor is exposed as a single Matter On/Off device named Computer Screen.
• The PC stays awake. Only the display power signal is toggled — the machine never sleeps, locks, or logs out, so it stays reachable on the network.
• Driven by the real display state. The actual Windows display state is written back to Matter, so a manual mouse/keyboard wake is reflected in Google Home.
• No DDC/CI dependency. Uses Windows display-power messages, so multiple monitors (including two Dell panels on the dev machine) switch together reliably.
• Fully local. Matter runs on your LAN via Google Home Mini as a Matter hub. After the one-time pairing, day-to-day commands never leave the network.
• Repeatable, auditable install. A single PowerShell installer configures the build, firewall, IPv6, and a logon scheduled task — and saves the original network state so uninstall can restore it.

How it works

flowchart LR
    Voice["Google Home Mini"] --> Hub["Google Home<br/>Matter Fabric"]
    Hub -->|"Local IPv6 / Matter"| Bridge["Matterbridge 3.9.0<br/>(plugin)"]
    Bridge -->|"JSON Lines over stdio"| Host["ScreenControl.Host.exe"]
    Host -->|"Windows power messages"| Displays["All connected displays"]

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• A Matterbridge plugin (TypeScript) publishes a standard On/Off Matter device to the Google Home fabric.
• A dedicated .NET 8 host (ScreenControl.Host.exe) does the interactive Windows display work and reports the true display state back over a simple JSON-Lines protocol.
• The plugin only updates Matter state after the host confirms the action. If the host stops unexpectedly, a supervisor rebuilds it and retries a command once — never in a loop.

Requirements

• Windows 11
• Node.js 24.x
• .NET 8 Desktop Runtime (or SDK)
• An Ethernet network interface that is connected
• The Google Home Mini and the PC on the same LAN that passes multicast / mDNS
• Administrator rights to run the installer

Matter requires link-local IPv6. The installer enables IPv6 on the chosen interface and sets its network category to Private. The original settings are saved so uninstall can restore them.

Installation

1. Get the code. Download the latest source from the Releases page (or git clone this repository) and extract it.

2. Run the installer from an elevated ("Run as administrator") PowerShell, in the repository folder:

   powershell.exe -NoProfile -ExecutionPolicy Bypass -File .\Install.ps1 `
       -InterfaceAlias 'Ethernet' `
       -Confirm:$false

   If your wired adapter is not named Ethernet, pass its name to -InterfaceAlias. Check with Get-NetAdapter.

The installer will:

1. Validate Windows, Node.js, .NET, and the network interface.
2. Save the current IPv6 binding and network category.
3. Enable IPv6 and set the interface to Private.
4. Create firewall rules limited to Private / LocalSubnet for UDP 5353 (mDNS) and 5540 (Matter).
5. Build and publish the Windows display-control host.
6. Build and install Matterbridge 3.9.0 and this plugin.
7. Install a launcher that waits for the interface and IPv6 to be ready.
8. Register a scheduled task that auto-starts after the current user signs in.
9. Run a five-second display self-test to confirm real control works.

Re-running the installer is safe: it stops the existing Matterbridge process tree, swaps the global package, and restarts the task. The network settings saved on the first run are never overwritten — to change interfaces, uninstall first.

Preview without changing anything:

powershell.exe -NoProfile -ExecutionPolicy Bypass -File .\Install.ps1 `
    -ValidateOnly `
    -InterfaceAlias 'Ethernet'

Add -SkipSelfTest to skip the five-second screen test.

First-time Matter pairing

1. Confirm the scheduled task Google Home Screen Control is running.
2. On this PC, open http://127.0.0.1:8283/.
3. The Matterbridge home page shows a Matter QR code and pairing code.
4. In the Google Home app, add a new Matter device and scan the QR code.
5. Add it to the same Home as the Home Mini, keeping the name Computer Screen.

This is a one-time secure commissioning. Signing in again or rebooting does not require re-pairing, and uninstall preserves the Matter pairing data by default.

Voice control

After pairing:

OK Google, turn off Computer Screen
OK Google, turn on  Computer Screen

Prefer your own phrasing? Create two Google Home Household Automations that map custom sentences (for example "turn off this computer screen") to Computer Screen Off/On. That only changes phrase parsing — the local control path is unchanged.

How it behaves

Turning off — The host broadcasts SC_MONITORPOWER = 2 so all displays stop their signal. The computer stays awake and Matterbridge keeps running.

Turning on — The host broadcasts SC_MONITORPOWER = -1 plus a momentary display-required signal. If Windows still reports the screen off after two seconds, it performs a single one-pixel mouse nudge (then returns the cursor) as a fallback wake.

Manual wake — Mouse or keyboard wakes the screens normally; the real Windows display state is written back to the Matter OnOff attribute.

Login session — Display control needs an interactive Windows session, so the task starts after the current user signs in (control is not available while signed out). On logon or power-state resume, Start-Matterbridge.ps1 waits for the interface to be Up with a preferred IPv6 address, then clears only the safe-to-rebuild Matter session/subscription caches — the Google Home fabric, commissioning, and access-control data are preserved. Node and the host run inside a JOB_OBJECT_LIMIT_KILL_ON_JOB_CLOSE Windows Job Object so nothing is orphaned if the task stops.

Diagnostics

Check the scheduled task:

Get-ScheduledTask -TaskName 'Google Home Screen Control' | Select-Object TaskName, State

Restart the background service:

Stop-ScheduledTask  -TaskName 'Google Home Screen Control' -ErrorAction SilentlyContinue
Start-ScheduledTask -TaskName 'Google Home Screen Control'

Inspect the plugin and logs:

matterbridge.cmd --list
Get-Content "$HOME\.matterbridge\matterbridge.log" -Tail 100
Get-Content "$env:LOCALAPPDATA\GoogleHomeScreenControl\launcher.log" -Tail 100

Verify the network state Matter needs:

Get-NetAdapterBinding   -Name 'Ethernet' -ComponentID ms_tcpip6
Get-NetConnectionProfile -InterfaceAlias 'Ethernet'
Get-NetIPAddress         -InterfaceAlias 'Ethernet' -AddressFamily IPv6

Run the five-second display test manually:

$hostPath = Join-Path (npm.cmd root --global) `
    'matterbridge-google-home-screen-control\bin\ScreenControl.Host.exe'
& $hostPath --self-test

Troubleshooting

• Google can't find the device during pairing — confirm the PC and Home Mini are on the same subnet, IPv6 is enabled on the interface, and the network category is Private. Re-run Install.ps1 -ValidateOnly to see the current state.
• Device shows offline after a reboot — the launcher waits for a preferred IPv6 address; give it a moment after sign-in, then check launcher.log.
• Wrong adapter — if your wired NIC isn't Ethernet, reinstall with the correct -InterfaceAlias.

Uninstall

Remove the service, plugin, and firewall rules, restore the pre-install IPv6 / network category, and keep the Matter pairing data:

powershell.exe -NoProfile -ExecutionPolicy Bypass -File .\Uninstall.ps1 -Confirm:$false

Other options:

.\Uninstall.ps1 -ValidateOnly                 # show the uninstall plan only
.\Uninstall.ps1 -RestoreNetwork:$false -Confirm:$false   # leave network settings as-is
.\Uninstall.ps1 -PurgeMatterData -Confirm:$false         # also delete all local Matter pairing data

-PurgeMatterData affects every Matterbridge pairing for the current Windows user. Use it only if you are sure none are still in use.

Security

• The admin front end binds to 127.0.0.1:8283 only — other LAN devices cannot open it.
• Firewall rules allow only Node.js to accept LocalSubnet UDP 5353/5540 on Private networks.
• No public ingress is created, and no Google password or OAuth token is stored.
• Matter pairing keys live in the current user's $HOME\.matterbridge and $HOME\.mattercert.

Design notes

A few decisions that shape the implementation:

• Local Matter instead of a cloud webhook. A cloud bridge or VPS would add public attack surface, account coupling, and ongoing upkeep for a one-machine convenience. Home Mini already speaks Matter on the LAN, so the screens are modeled as a standard On/Off device.
• Keep awake, switch only the display signal. Letting Windows sleep can make it impossible to wake the display from the network. The system stays awake and only toggles monitor power.
• Trust the OS, not the command. Treating a command as the source of truth reports the wrong state after a manual wake, so the host monitors the real display state and reports it back. GUID_CONSOLE_DISPLAY_STATE is not used to gate the wake fallback because it can stay true after a monitor is off.
• One ownership boundary. Command execution stays in the plugin; the Matter attribute transition is owned by Matterbridge's OnOff behavior. The plugin does not write the command-owned attribute itself, which previously caused commands to fail after Windows had already acted.
• A windowless launcher owns the process tree. A .NET 8 WinExe launcher runs as the interactive scheduled task (no console window) and assigns PowerShell → Node → Matterbridge → host to a kill-on-close Job Object, giving Task Scheduler deterministic ownership for restart and cleanup.
• Wait for IPv6, drop only session cache. On resume, starting Matterbridge before IPv6 is ready — or loading a stale Matter session cache — can make Google Home briefly unreachable. The launcher waits for a preferred IPv6 address and clears only session/subscription caches, never the fabric or credentials.

Project structure

.
├── Install.ps1               # Repeatable build / network / firewall / scheduled-task install
├── Uninstall.ps1             # Uninstall and restore saved network settings
├── Start-Matterbridge.ps1    # Wait for network readiness, prune session cache, start Matterbridge
├── GoogleHomeScreenControl.sln
├── plugin/                   # Matterbridge DynamicPlatform plugin (On/Off Plug-In Unit)
│   └── src/
└── src/
    ├── ScreenControl.Host/       # Windows display control, wake lock, state monitor
    └── ScreenControl.Launcher/   # WinExe launcher owning the kill-on-close Job Object

Contributing

Issues and pull requests are welcome. See CONTRIBUTING.md for the development setup and build/type-check commands.

License

MIT © Alone