Monitor Switcher

A tiny, dependency-free Windows system-tray app that changes your primary monitor instantly with a global hotkey.

Switching the primary (main) display is what moves the taskbar, newly opened windows and the Alt-Tab switcher onto that screen. Windows has no built-in shortcut for it — Monitor Switcher adds one.

Built for the classic multi-monitor split: a desk monitor and a TV on the couch. Tap a hotkey to make the TV your main screen when you sit down, and tap another to hand it back to the desk when you get up.

Features

• Global hotkeys — Ctrl+Alt+1 … Ctrl+Alt+4 make that monitor primary from anywhere.
• Tray menu — right-click to pick a display, identify monitors, toggle start-with-Windows, or exit.
• Identify monitors — flashes a big number on each screen so you know which index maps to which physical display (double-click the tray icon, too).
• No third-party dependencies — pure Win32 APIs. No AutoHotkey, no drivers, no downloads.
• Reliable on Windows 10/11 — uses the modern CCD display API (SetDisplayConfig), which actually commits the change where the legacy ChangeDisplaySettingsEx path silently fails on modern Windows.
• Lightweight — single instance, ~150 KB exe, sits quietly in the tray.

Requirements

• Windows 10 or 11.
• .NET SDK 9 to build the project, or just the in-box .NET Framework (the build.ps1 fallback needs nothing extra).

Build

Either build the .NET project:

dotnet build MonitorSwitcher.sln -c Release
# output: bin\Release\net9.0-windows\MonitorSwitcher.exe

…or, if you don't have the SDK, use the zero-dependency script that compiles with the C# compiler already shipped in Windows:

powershell -ExecutionPolicy Bypass -File .\build.ps1
# output: .\MonitorSwitcher.exe

Usage

Run MonitorSwitcher.exe. A small monitor icon appears in the system tray.

Action	What it does
Ctrl+Alt+1 … Ctrl+Alt+4	Make monitor #1–#4 the primary display
Right-click tray icon	Open the menu (pick a monitor, identify, startup, exit)
Double-click tray icon	Identify monitors (flash each screen's number)

Not sure which number is which screen? Use Identify monitors — the index it shows is the same number you press with Ctrl+Alt.

Start with Windows

Right-click the tray icon → Start with Windows. This adds a per-user entry under HKCU\…\Run (no admin required); toggle it off to remove it.

How it works

Concern	Approach
Enumerate displays	EnumDisplayDevices + EnumDisplaySettings
Set the primary monitor	CCD API: QueryDisplayConfig → shift every source so the target lands at (0,0) → SetDisplayConfig
Global hotkeys	RegisterHotKey on a message-only window
Identify overlay	Borderless top-most WinForms windows, auto-closed by a timer
Run at login	HKCU\Software\Microsoft\Windows\CurrentVersion\Run

On Windows 10/11 the legacy ChangeDisplaySettingsEx call validates a mode but refuses to commit a primary/topology change (returns DISP_CHANGE_FAILED), so this app uses the newer Connecting and Configuring Displays (CCD) API instead. The primary display is, by definition, the source at coordinate (0,0), so making a monitor primary means translating every display so the chosen one sits at the origin.

Configuration

The hotkeys and how many of them are registered live in TrayContext.cs:

• MaxHotkeys — how many Ctrl+Alt+<n> hotkeys to register.
• The keys array (Keys.D1 … Keys.D4) and the mods (MOD_CONTROL | MOD_ALT) — change these to use different keys or modifiers.

Rebuild after editing.

Project structure

File	Responsibility
Program.cs	Entry point, single-instance guard, DPI awareness
TrayContext.cs	Tray icon, menu, hotkey wiring
MonitorService.cs	Enumerate displays and set the primary
CcdNative.cs	Modern CCD (SetDisplayConfig) implementation
HotKeyManager.cs	Global hotkeys via a message-only window
NativeMethods.cs	Win32 P/Invoke signatures and structs
IdentifyOverlay.cs	The "identify monitors" overlay
StartupManager.cs	Run-at-login toggle
build.ps1	SDK-free build using the in-box C# compiler

License

MIT