Turn an iPad or iPhone stuck on iOS 12 into a second display for your Mac (macOS 26), over Lightning or Wi-Fi — free, self-hosted

Built and running for real on an iPad Air (Model A1475, iOS 12.5.8), over a Lightning cable and over Wi-Fi. H.264 video, touch, two-finger scroll, and a real mouse cursor all work.

Free alternative to Sidecar (iOS 13+), Duet Display, and Luna Display for a device that cannot run OpenDisplay's own client (that client needs iPadOS 17+). The Mac app is unmodified OpenDisplay (GPL-3.0): it creates the virtual display, captures it, encodes H.264, and sends it over USB (usbmuxd) or Wi-Fi (Bonjour). No iproxy. The iOS/ app is a clean-room iOS 12 client of that same protocol (MIT).

Same Wi-Fi is enough. Plug in a Lightning cable for better speed and quality: the Mac prefers USB (lower, steadier latency) and falls back to Wi-Fi when the cable is pulled.

iPhone uses the same project. Pick it as the Xcode destination. The screen is smaller, so an iPad is the useful case. Minimum iOS is 12.0 (iOS/project.yml → deploymentTarget), tested on iOS 12.5.8.

iOS/LegacyPadDisplay.xcodeproj is ready to open. iOS/project.yml is the XcodeGen source of truth (xcodegen generate after you edit it). The client lives in iOS/App/ (VideoReceiver.swift listens on port 9000, decodes H.264, and sends touch, scroll, and cursor messages). Mac/ is a git submodule of upstream OpenDisplay, unmodified, so git submodule update --remote picks up their releases.

git clone --recurse-submodules https://github.com/cuongpham1/ipad-iphone-second-monitor-ios12-free.git
cd ipad-iphone-second-monitor-ios12-free

If you already cloned without --recurse-submodules:

git submodule update --init --recursive

• Prebuilt (recommended): download OpenDisplay.dmg from the latest release and drag OpenDisplay.app into /Applications before launching. macOS ties Screen Recording and Accessibility to that path. Launching from the disk image, then moving the app, means granting both permissions again, and the volume unmounts on reboot.
• From source: open Mac/ in Xcode and run it. See OpenDisplay's build instructions.

On first launch, grant Screen Recording and Accessibility (System Settings → Privacy & Security). Fully quit the app (Cmd+Q) and relaunch it. Flipping the toggle is not enough; the app reads the new permissions on restart.

open iOS/LegacyPadDisplay.xcodeproj

In Xcode:

1. Select target LegacyPadDisplay → Signing & Capabilities → set Team to your personal Apple ID.
2. Copy the iOS 12.5 DeviceSupport profile (next section) if the iPad is not already a Run destination.
3. Plug the iPad in with a Lightning cable, select it in the toolbar, and hit Run.
4. On first install, on the iPad open Settings → General → VPN & Device Management and trust your developer certificate.

The app should show a fullscreen black screen with "Listening on :9000" at the bottom. It is waiting for the Mac.

Recent Xcode builds do not ship iOS 12 device support. Without this folder the iPad does not appear as a Run destination, and Xcode reports "Failed to prepare the device for development". Copy the 12.5 profile from apptim/iPhoneOSDeviceSupport:

curl -L -o /tmp/12.5.zip https://raw.githubusercontent.com/apptim/iPhoneOSDeviceSupport/master/12.5.zip
unzip -o /tmp/12.5.zip -d /tmp/ds125
cp -R "/tmp/ds125/12.5" ~/Library/Developer/Xcode/iOS\ DeviceSupport/

A plain 12.5 folder is enough for 12.. filsv/iOSDeviceSupport has other versions. Quit Xcode fully, reconnect the iPad, and reopen the project.

This is an Apple limitation, not something this project can fix. After 7 days, plug the cable back in, open Xcode, and hit Run again to reinstall. To avoid repeating this, you'd need a paid Apple Developer Program membership ($99/year) — signs for a full year.

Leave both apps running (Mac permissions granted and the app relaunched; iPad app open).

• Cable: plug the iPad into the Mac. OpenDisplay finds it through usbmuxd on port 9000, same as its own client.
• Wi-Fi: same network, no cable. The Mac browses for _opensidecar._tcp and connects to port 9000. Allow Local Network on the iPad the first time.

The iPad should switch from black to the macOS desktop, with a mouse cursor. A new display appears under System Settings → Displays. Drag a window onto it.

• No new display under System Settings → Displays: Screen Recording or Accessibility is missing, or the Mac app was not fully quit and relaunched after you granted them (Step 1).
• The Mac app's console (Xcode → View → Debug Area → Console, scheme OpenSidecarMac) shows whether it sees the device over usbmuxd.
• A black frame for a second after you switch back to the iPad app is the reconnect. The listener stops in the background, and ensureListening() starts it again when the app returns.
• An updateRequired message means a newer OpenDisplay changed the protocol. VideoReceiver.swift omits the pv field, so the Mac treats this client as protocol 1, which current OpenDisplay releases still accept.

Works: video, touch to click and drag, two-finger scroll, a mouse cursor (position and shape), and reconnect when the app returns to the foreground (a short flicker).

Missing: an external keyboard, automatic rotation to match the virtual display, latency measurement.

• iOS/ (this client): MIT, see LICENSE.
• Mac/: submodule of peetzweg/opendisplay, GPL-3.0, copyright held by its authors. Unmodified, not vendored into this repo.

Keywords: iPad iOS 12 second monitor Mac, old iPad external display, Sidecar alternative iOS 12, Duet Display free alternative, Luna Display free alternative, OpenDisplay iOS 12 client, Lightning USB second screen, legacy iPad second monitor, LegacyPadDisplay.