A free Mac app for parents
Explicit content on your Mac, covered the moment it appears.
SentryScreen is a small app for your family's Mac. It checks what is on the screen, on the Mac itself, and drops a solid cover over explicit content in any app or browser. Free and open source.
Free · open source (AGPL-3.0) · for Mac
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Nothing from your screen leaves the Mac
The screen is checked on the Mac, in memory. The app never keeps, uploads, or sends screen images. (A developer command-line option you run yourself can save crops; see Privacy.)
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Your child cannot remove it or change its settings
Settings need your PIN and removal needs the administrator password. Protection starts again at every login. The one way around it is under Honest limits.
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Free, and the code is open
No account, no subscription, no trial. Every line of the app and the detector it runs is published under AGPL-3.0. Read the source
What it does
The whole screen, not just the browser
The cover is a plain solid rectangle. Nothing shows through it, it moves with the window underneath, and it says nothing more than “Content blocked”.
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In a browser
A page scrolls, a picture comes into view, and the cover lands on it. It stays on the picture as the page keeps scrolling.
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It follows the window
Drag the window across the desk and the cover rides along. Nothing shows through at any point.
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In a chat, or any other app
It is not a list of blocked websites. A picture sent in a chat is covered the same way, in an app we have never heard of.
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The whole window, if it has to
If a cover stays up for a while, the whole window is covered until the content is gone or the window is closed.
Setup
Three things you do, once
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Install it
Download the newest release from GitHub and run the installer from an administrator account on the Mac.
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Set a parent PIN
The PIN keeps settings with you. It is the first thing setup asks for.
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Grant permission
macOS makes you switch on Screen Recording by hand, in System Settings. No app can do it for you. Setup shows you exactly where the switch is. Protection starts as soon as it is on.
Why we built it
For parents who are done worrying
SentryScreen was built by a parent of eight who was tired of the usual routine:
- the router settings and the DNS blockers,
- the maze of Apple's parent and child restrictions,
- the checking and worrying that never ended, all so the kids could use a computer.
What we believe
- No child can be shielded from explicit content every second of every day.
- Exposure can be cut sharply, without a parent standing behind the chair.
- One detector on the Mac itself, covering whatever appears on the display, is how. Let the Mac keep watch.
Honest limits
What it does not do
Better said before you install it than after.
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It reacts, it does not prevent
Content can be on screen for a fraction of a second before the cover lands, and longer if it slides in from the edge of a window.
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It can miss things, and it can cover harmless things
It is a detector, not a person. It can cover something harmless, and it can miss something. One layer of protection, not the whole answer.
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Explicit means nudity and sexual images
It does not look for violence or words.
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It covers what is on the screen, and that is all
It does not block websites, filter downloads, restrict apps, or read messages. Video from protected streaming services such as Netflix is hidden from every app by macOS, so it is not covered.
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A Standard account can switch off its screen permission
macOS lets any account reset the Screen Recording permission with a Terminal command and no password. SentryScreen then stops covering on that Mac until you turn the permission back on in System Settings › Privacy & Security.
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It protects one screen
If a second screen is connected to the Mac, anything shown on it is not covered. The menu names the screen that is protected.
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Going fullscreen shows the window for a moment
When a window enters or leaves fullscreen, macOS draws its animation above everything, our cover included. For about half a second the window shows, then it is covered again on its own.
Download
Free, and open source
No account, no license key, nothing to sign up for.
Download the app
One click downloads the installer for the newest version. Open it and follow the steps. New versions are not installed for you: come back here when you want the next one.
Download for MacBuild it yourself
The app, the detector’s model weights, and the code that trains and exports them are all in one repository, with build steps in its README.
Build from source- Licensed under the GNU Affero General Public License, version 3. Use it on as many Macs as you like.
- The app and the model weights are published. The images the model was trained on are not.
- The tuning tools are in every build: adjust detection on your own Mac, and see what the detector sees.
Help out
Help make it better
SentryScreen improves when the people who use it speak up.
Tell us what it missed
If something slipped through, or a cover landed where it should not have, open an issue. A diagnostic report, which you read before it is sent, helps us find the cause.
Open an issueImprove the code
Developers are welcome: detection, covers, the setup flow, the docs. The contributing guide has the build steps and the few rules the project keeps.
Contributing guide- SentryScreen stays free either way. If it helps your family and you would like to chip in, you can support the project. Contributions are not tax-deductible.
Questions
Before you install
Can my child turn it off?
Not without your PIN or your password, with one gap. Settings need your PIN. Removing it, or clearing the covers for a few minutes, needs the Mac’s administrator password, which should be yours alone. One gap: on a Standard account, a child who knows the Terminal command can switch off SentryScreen’s Screen Recording permission without a password, and SentryScreen stops covering until you turn the permission back on.
What permission does it need, and why?
One: Screen Recording, which is how macOS lets an app see what is on the screen. You grant it by hand in System Settings › Privacy & Security during setup. Nothing is recorded. The name is Apple's, not a description of what SentryScreen does.
Does it send anything over the internet?
Only one thing, and only if you choose to: a diagnostic report. You see what is in it, and nothing is sent until you approve it on that Mac. It is never sent automatically and never contains screen content. The privacy page lists what a report holds and how long it is kept.
How do updates work?
The app does not update itself or check for updates. The Download button on this site always gets the newest version; open it and the installer replaces the old one. Notes on what changed are on the releases page.
How many Macs can I use it on?
As many as you like, with as many child accounts on each as you need. Your child’s account must be a Standard account, not an administrator one: an administrator can remove SentryScreen or clear its covers.
Can a school, library or business use it?
Yes. The license is AGPL-3.0: you can use, change and share it. If you share a changed version, or offer it to others over a network, you share your changes under the same license.
Something is wrong. Where do I ask?
Open an issue on GitHub, or see the Support page.