I have a function in my app to detect if screens are added or removed, watching for notifications from NSApplication.didChangeScreenParametersNotification. I am seeing some strange behavior when the screen attached to a Mac mini is turned off, macOS will spit out hundreds of the didChangeScreenParametersNotification, all relating to a 'ghost' screen being added and then subsequently replaced with the original screen a second later. This cycle will go on for hours until the screen is turned back on again. I can confirm this also happens with the CoreGraphics equivalent, with flags .added and .removed being the only changes. I would imagine this creates immense churn for all apps watching for screen changes. I've tried debouncing the notifications but even with a delay of 10 seconds this is still being called hundreds of times while the computer is idle and the screen is off. One constant I can see is that the CGDisplayUnitNumber() for the 'ghost' display is always 0, while the logical unit number for the real screen is '1'. Is it safe to ignore screens with 0? I'm trying to find a reliable way to prevent heavy processing for 'false' screens. I'm afraid because this ghost screen has parameters so different to the actual screen, it's otherwise not possible to ignore it as it looks like a new screen. See example below: // Observe notification NotificationCenter.default.addObserver(self, selector: #selector(displaysDidChange), name: NSApplication.didChangeScreenParametersNotification, object: nil) // Function to update screens called from displaysDidChange func updateScreens() { let screens = NSScreen.screens for screen in screens { guard let screenDisplayID = screen.displayID() else { NSLog("Screen does not have a display ID: \(screen.localizedName)") continue } let screenIdentifier = "v\(CGDisplayVendorNumber(screenDisplayID)), m\(CGDisplayModelNumber(screenDisplayID)), sn\(CGDisplaySerialNumber(screenDisplayID)), u\(CGDisplayUnitNumber(screenDisplayID)), sz\(CGDisplayScreenSize(screenDisplayID))" } // -- Logic to determine if screen is new or already exists for window management -- NSLog("Found new screen display ID \(screenDisplayID) (\(screenIdentifier)): \(screen.localizedName)") } And the logging I'll get: Found new screen display ID 2 (v16652, m1219, sn16843009, u1, sz(1434.3529196346508, 806.823517294491)): Philips FTV Found new screen display ID 10586 (v1970170734, m1986622068, sn0, u0, sz(677.3333231608074, 380.9999942779541)):