What happens if someone force quits a Mac screen locker

It depends on the locker. A screen locker is usually an ordinary app that draws a window over your desktop, and unless it was built for this, an app that is force quit, crashes or is stopped from Terminal takes its window with it, leaving whatever was underneath on show. A locker built to hold hands over to the macOS lock the moment it is closed, so the desktop never appears. The macOS lock screen itself is not an app in the Force Quit list, which is why it makes the right backstop.

This post covers why the difference exists, how to test any locker on your own Mac in a few minutes, and what macOS does in the worst cases.

Why a screen locker is not the macOS lock

The lock you get from Control-Command-Q, or from Lock Screen in the Apple menu, is run by macOS. It does not appear in the Force Quit window, and nothing in your Dock is holding it up.

A screen locker app is different. It is an app you opened, running in your session alongside everything else. To cover the screen, it draws windows over every display and tries to keep the keyboard and pointer to itself. How well it does that is up to the app, and so is what happens when it stops.

An app can stop while the screen is locked in several ways:

• Force Quit. Option-Command-Escape opens the Force Quit window, and Force Quit in the Apple menu does the same. Anyone at the keyboard who can reach that window can quit the locker.
• A crash. Any app can crash, and a locker is no exception.
• Terminal or a remote login. If Remote Login is turned on in System Settings, under General, then Sharing, someone with an account can stop processes from another computer.
• Updates. An app that restarts itself to update has a moment when it is not running.

None of these are exotic. The question is not whether a locker can be closed, but what is on the screen in the moment after.

How to test a screen locker yourself

You can check any locker in a few minutes. Close anything private first, and do it on your own Mac.

1. Open TextEdit and leave a blank document in front.
2. Lock the screen with the locker.
3. Type a few words. Then try Command-Tab and Command-Q.
4. Press Option-Command-Escape. If the Force Quit window appears, select the locker and click Force Quit.
5. Look at what comes up. The macOS lock screen is a pass. Your desktop is a fail.
6. Unlock and look at the TextEdit document. Any words in it reached your apps while the screen was supposedly locked.

While you are at it, check a few other things:

• Plug in a monitor while locked and see whether it is covered as soon as it lights up.
• Type a wrong password several times. Does anything slow the guesses down, and does the app tell you about them afterwards?
• Look at which permissions the app asked for, and whether your password is checked by macOS or by the app itself.

What macOS does in the worst cases

Some protections come from macOS whatever locker you use, and they are worth setting up first.

• Holding the power button. The Mac turns off, unsaved work is lost, and nothing is shown. At the next start, macOS asks for your password at the login window.
• FileVault. In System Settings, under Privacy & Security, FileVault encrypts the startup disk, so it cannot be read until someone logs in with your password. Turn it on if it is off.
• Waking from sleep. In System Settings, under Lock Screen, set “Require password after screen saver begins or display is turned off” to Immediately, so a sleeping Mac never wakes straight to your desktop. Require a password immediately after a Mac sleeps explains the trade-offs.

These cover a Mac that is turned off or asleep. A locker covers the time in between, when the Mac is on, your apps are open and you have stepped away.

How Shoji handles being force quit

Shoji is a privacy screen for the Mac: press Command-L and a screen slides shut over everything on every display, and Touch ID or your Mac password, checked by macOS, opens it again. Here is how it answers the test above.

A guard runs beside it. If anything closes Shoji while your Mac is locked, even Force Quit, the guard turns on the macOS lock before the desktop can show. Whoever quit it ends up at the real macOS lock screen, which needs your password or Touch ID, and your apps are still open behind it, because turning on the macOS lock does not quit them.

The rest of the design covers the other checks:

• While the screen is shut, the keyboard belongs to the lock, so nothing typed reaches your apps.
• A monitor plugged in while locked is covered the moment it wakes.
• Each wrong password makes the next try wait longer, and you see every failed try when you come back.
• After an away time you choose, it turns on the macOS lock on its own, so a long absence ends behind the heavier door anyway.
• Your password goes straight to macOS and is never stored, logged or sent. It asks for no Screen Recording, Accessibility or Full Disk Access permission, since it never captures the screen or reads windows.

The limits are worth stating. Shoji is a screen over your Mac, not protection against malware, cameras, screen recording by other apps or network snooping. Its quick blur mode has no password by design (esc brings the screen back), so it is for someone glancing over your shoulder, not for walking away. And once the guard hands over, the macOS lock is in charge, with the protections above.

Shoji is $14 once and free for 24 hours, on macOS 14 or later, Apple silicon and Intel. That is enough time to run the test above on it yourself.

Questions

Can someone force quit the macOS lock screen? It is not an app in the Force Quit list, so there is nothing there to quit. That is why a well-built locker treats the macOS lock as its fallback.

Will I lose open work if a locker hands over to the macOS lock? No. Turning on the macOS lock does not quit your apps. Unlock as usual and everything is still open.

Is holding the power button a way around a locker? It turns the Mac off, so nothing on the screen is revealed, but unsaved work is lost. At the next start, macOS asks for your password, and with FileVault on, the disk stays unreadable until then.