OnAirScreen is not signed with an Apple Developer ID certificate, so macOS treats every downloaded copy as untrusted until you explicitly allow it.

• Gatekeeper checks apps before they run.
• Downloaded files get the extended attribute com.apple.quarantine.
• Without a trusted signature, macOS refuses to start the app.
• Removing the quarantine flag tells macOS you trust this copy.

This is normal for unsigned open-source macOS apps — not a sign that OnAirScreen is broken.

Option A — Terminal (recommended)

Open Terminal (Applications → Utilities → Terminal) and run:

sudo xattr -d com.apple.quarantine /Applications/OnAirScreen.app

Enter your Mac password (nothing appears while typing — that is normal).

Then start OnAirScreen from Applications or Launchpad.

Option B — Finder (without Terminal)

1. Drag OnAirScreen.app from the DMG to Applications
2. Right-click (or Control-click) OnAirScreen.app → Open
3. In the dialog, click Open again to confirm
4. macOS remembers this choice for future launches

Check whether the quarantine flag is still set:

xattr -l /Applications/OnAirScreen.app

If removal worked, com.apple.quarantine should not appear in the output.

"No such xattr: com.apple.quarantine" The flag is already removed — try launching the app normally.

"Operation not permitted"

• Confirm the path: /Applications/OnAirScreen.app
• Use sudo as shown above
• On corporate Macs, admin rights or MDM policies may block this

App still won't start

• System Settings → Privacy & Security — look for Open Anyway
• Ensure you copied the app to Applications, not running it directly from the DMG