Hide Slack, Messages and Mail when someone walks up to your Mac

20 October 2026 · 6 min read

To hide messages on a Mac screen, deal with the two places they appear: notification banners and the app windows themselves. Set notification previews to Never in System Settings, and get used to Command-H, which hides the app in front in one keystroke. If you want Messages, Slack and Mail to stay open but unreadable to anyone but you, an app such as Shoji can keep those three blurred unless you are the one using them.

The rest of this guide goes through where conversations leak onto the screen, what macOS can do about each one, and where it runs out.

Where your messages show up without you asking

Most people think of the chat window, but there are several places a private line of text can appear while someone is standing at your desk.

Notification banners. A new message slides in at the top right, with the sender and the first part of the text. This is the one that catches people out, because it appears on its own while you are doing something else.
Notification Center. Older banners stay in the list until you clear them.
The chat window behind your work. Messages shows the latest line of every conversation in its sidebar. Slack shows whole channels. Mail shows senders, subjects and preview lines in the message list.
A second display. If Slack lives on your external monitor all day, anyone standing behind you can read it, even when your main screen shows something harmless.
Dock badges. A badge only shows a count, but it tells someone a conversation is waiting.

Each of these needs a different fix, so it helps to take them one at a time.

Stop previews in notifications

This is the single most useful setting, and it takes a minute.

Open System Settings and choose Notifications.
At the top, set Show previews to Never. A banner then says a message arrived from an app but not what it says. When Unlocked does not help with this problem: when someone walks up, you are at the Mac and it is unlocked, so the preview shows.
To be stricter for one app, click it in the list below (Messages, Slack or Mail) and set its own preview option, or set its alert style to None so nothing slides in at all.

The same screen has switches for whether notifications appear while the screen is locked, while the display is asleep and while you are mirroring or sharing the display. If you ever present from your Mac, turn the sharing one off.

For a quieter hour, turn on a Focus from Control Center. Do Not Disturb holds notifications back until you turn it off, so nothing appears while someone is looking at your screen with you. Slack and Mail also have notification settings of their own, so if banners still appear, look inside each app’s settings as well.

Mail can show fewer preview lines in its message list, or none, which leaves senders and subjects only. Look in Mail’s settings if you want the list less revealing.

Get a chat window out of sight quickly

Notifications are the passive problem. The open window is the active one, and macOS gives you a few fast ways to get rid of it.

Command-H hides the app in front. Its windows disappear, and it keeps running. Click its Dock icon to bring it back.
Option-Command-H hides every app except the one in front. Useful when the thing you want to keep on screen is your document and everything else should go.
Command-M minimizes the current window to the Dock, if you prefer to bring back one window rather than the whole app.
A Space of its own. Put your chat apps on a separate desktop in Mission Control, and switch away from it with Control and an arrow key, or a swipe with three or four fingers depending on your trackpad settings.

These all work, and they cost nothing. Their weakness is timing. You have to notice the person, decide which app is the risky one and press the keys, and by then someone who walked up quietly may have read the last line already. They also undo themselves the moment you switch back to the app, so a chat can be fully readable again while the other person is still there.

Keep the chat apps blurred unless you are using them

Shoji is a privacy screen for the Mac, and one of its five modes is built for this problem: Messages, Slack and Mail stay blurred unless you are the one using them. You do not have to react to anyone. The apps sit on your screen, open and up to date, but softened so the text cannot be read. When you switch to one of them it is sharp again, and when you switch away it softens.

If you only want a quick look at a chat without bringing it to the front, hold Option over it to peek.

For the moment someone walks up while a chat is the window you are using, there is a second mode: a quick blur of everything, with no password. One shortcut softens the whole screen, and esc brings it straight back. You can also set a hot corner to blur, so a flick of the pointer does it without the keyboard.

Two details matter for a privacy tool that sits over your messages:

The blur is drawn by macOS itself. Shoji never captures the screen or reads what is in your windows, so it needs no Screen Recording, Accessibility or Full Disk Access permission.
It goes online only to activate the license and check for updates. There is no account and no analytics.

What it does not change is your notification settings. Whether a banner shows a preview is still decided by macOS, so set Show previews as described above as well. The blur mode covers Messages, Slack and Mail by name. For anything else, use the quick blur of the whole screen, Command-H, or Focus Blur, which keeps only the window you are using sharp.

A routine that holds up in a busy room

Put the pieces together and you get something that works without thinking about it:

Set Show previews to Never, once.
Keep chat apps on their own display or Space if you can.
Keep Messages, Slack and Mail blurred unless you are using them, so the open windows give nothing away.
When someone walks up, use the quick blur or Command-H, depending on what you have in front.
When you step away, lock the whole screen. Shoji’s Command-L slides a screen over every display, and Touch ID opens it with every window where you left it.

Shoji is $14 once and free for 24 hours, on macOS 14 or later.

Questions

Can I hide message previews for Messages only? Yes. In System Settings, open Notifications, click Messages in the list of apps and change its preview option. Other apps keep their own setting.

Does hiding an app with Command-H stop its notifications? No. A hidden app keeps running, and its banners still appear. Use the preview setting or a Focus such as Do Not Disturb to control banners.

Does a blurring app need to read my messages to blur them? Not this one. The blur is drawn by macOS, and the app never reads what is in your windows, which is why it needs no Screen Recording permission.

Will people still see that I have unread messages? The Dock badge still shows a count unless you turn off badges for that app in Notifications settings. The count does not reveal the sender or the text.