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For 27″ 5K iMacs (2015 and later) · Apple silicon Macs

Your 5K iMac is a display again.

The simplest way to make your old iMac behave like a real external display. Plug in one Thunderbolt cable, and the iMac's keyboard, mouse and speakers come along too.

$9.99 One-time price. Yours to keep.Try it free for 7 days first · no subscription
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No card for the trial: enter your email and the download link arrives right away. Check that your Macs are supported first.

Real footage, my desk: plug in the cable, and the iMac becomes the MacBook's screen.
5120 × 2880Native 5K, pixel for pixel
LosslessText as crisp as your MacBook. Fast video can stutter.
One cableThunderbolt 3 or 4, nothing else to buy
Lid closedDock it and forget it
How it works

Two small apps and one cable.

Apple dropped Target Display Mode years ago, so a perfectly good 5K panel just sits there. Re5k brings that feature back in software. Your MacBook sees a real 5K monitor, and the iMac shows it.

  1. Install both apps

    Open the Re5k download from your email (the free trial is the full app). Drag Re5k (MacBook) to Applications on your Mac, and Re5k (iMac) on the iMac.

  2. Plug in the cable

    Connect a Thunderbolt cable directly between the two Macs, with no hub or dock in between. Open both apps.

  3. Follow the green lights

    Both Macs show a checklist with a green or red light for each permission and setting, and a button for each fix. The iMac shows its list on its screen while it waits. On your Mac, it opens the first time. If you don't see it, click the Re5k icon in the menu bar at the top of the screen and choose Setup Check…. Once everything is green, the iMac is your display.

A 27-inch iMac showing the Re5k checklist with green lights for Accessibility, Lock screen, Universal Control and Open at login, and a red light for the Thunderbolt cable, which is lying unplugged in front of it. A closed MacBook stands in a vertical dock beside it.
The iMac's checklist, waiting for the cable. Plug it in and the last light turns green.
What you get

It behaves like a monitor you plugged in.

A real second display

Arrange it in System Settings, drag windows onto it, use Mission Control and full-screen apps. It shows up as a 5K HiDPI screen that looks like 2560 × 1440.

Keep your keyboard and mouse

Keep them paired to the iMac. While your MacBook is connected, they control the MacBook. Unplug it and they control the iMac again. No Bluetooth re-pairing.

Sound from the iMac

Your Mac's audio plays through the iMac's speakers, and the iMac's volume keys control it.

Sleeps and wakes together

When your MacBook's screen sleeps, the iMac's goes dark too. Press a key and both wake up.

Lid closed

Plug your MacBook into power, close it, and tuck it away. The iMac becomes its only screen.

Starts on its own

Both apps open at login and reconnect when you plug in. A short unplug doesn't scatter your windows.

Compatibility

Will it work with my Macs?

You need two things: an iMac that runs macOS 12 Monterey or newer, and a Mac with Apple silicon. To check your iMac, choose Apple menu → About This Mac.

The iMac (your display)

ModelNewest macOSStatus
iMac 27″ 5K, 2020macOS 26Supported
iMac 27″ 5K, 2019macOS 15Supported
iMac 27″ 5K, 2017macOS 13Supported
iMac Pro 27″ 5K, 2017macOS 15Supported
iMac 21.5″ 4K, 2017 and 2019macOS 13 / 15Untested
iMac 24″ with Apple siliconcurrentUntested
iMac 27″ 5K, Late 2015macOS 12Thunderbolt 2
iMac 27″ 5K, Late 2014 and Mid 2015macOS 11Not supported

Late 2015 5K iMacs have the older Thunderbolt 2 port, so you'll need Apple's Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter plus a Thunderbolt 2 cable. Thunderbolt 2 is half the speed, so text and desktop work stay just as sharp, but video and fast scrolling are choppier than on a 2017 or newer iMac. These and the untested models should work, since the iMac app adapts to its screen size. The free trial is the way to find out on your own iMac before you pay. The 2014 and Mid 2015 iMacs stop at macOS 11, which is too old for Re5k.

The Mac you're connecting

  • Any Mac with Apple silicon (M1 or later): MacBook Air, MacBook Pro, Mac mini or Mac Studio.
  • macOS 13 Ventura or newer.
  • macOS 14.2 or newer for sound on the iMac.
  • Intel Macs can't drive the iMac.

You can switch between several Macs, such as a work laptop and a home laptop, one at a time. Install Re5k (MacBook) on each.

USB devices stay with the iMac. Re5k carries the picture, sound, keyboard and mouse. A printer, drive or cutter plugged into the iMac isn't passed through to your Mac. Share printers over the network, or plug other devices into your Mac. See Troubleshooting below.

Cables

Use a real Thunderbolt cable.

The cable carries the whole 5K picture, so it matters more than anything else. A charging cable that came with a phone or laptop won't work. First, find your iMac below. Not sure which one you have? On the iMac, choose Apple menu → About This Mac.

Thunderbolt 3 iMac 2017, 2019, 2020 or iMac Pro

  • You need: one Thunderbolt cable. That's it.
  • USB-C on both ends. Plug one end into your MacBook and the other into either of the two USB-C/Thunderbolt ports on the back of the iMac.
  • Full speed: the smoothest picture Re5k can do.

Thunderbolt 2 iMac Late 2015

  • You need two things: Apple's Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter (about $49 from Apple) and a Thunderbolt 2 cable (Apple or OWC).
  • This iMac has the older, smaller Thunderbolt 2 ports, so a USB-C cable won't fit it.
  • How it connects: MacBook → adapter → Thunderbolt 2 cable → iMac. The adapter plugs straight into your MacBook.
  • Half the speed of Thunderbolt 3: text and everyday work look just as sharp, but video and fast scrolling are choppier. Not tested on a Late 2015 iMac yet, so try the free trial before you buy anything else.

Choosing the Thunderbolt 3 cable

Use These work

  • Thunderbolt 3, 4 or 5 cable with the lightning-bolt logo on the plug, rated 40 Gb/s or faster.
  • Up to about 1 m for a regular (passive) cable. For a longer run, get an active Thunderbolt 4 cable, up to 2 m.
  • Good brands include Apple, OWC, CalDigit, Anker and Cable Matters. Check that the listing says Thunderbolt 4 or Thunderbolt 3, 40 Gb/s.

Avoid These don't

  • USB-C charging cables. Most only carry USB 2 speed, so the cable link never comes up.
  • Hubs, docks or adapters between the two Macs. Connect the cable directly to both. The one exception is Apple's Thunderbolt 2 adapter for a Late 2015 iMac.
  • USB-A adapters, or plain Mini DisplayPort cables. Those look like Thunderbolt 2 cables but carry no data. A real Thunderbolt 2 cable has the lightning-bolt logo on the plug.
  • Ethernet or Wi-Fi. Re5k only uses the cable, on purpose: Wi-Fi is far too slow for lossless 5K.

How to tell the cable is working: on either Mac, open System Settings → Network. Thunderbolt Bridge should show a yellow dot and “Self-Assigned IP.” If it says Inactive, unplug the cable for five seconds and plug it back in. If that doesn't help, the cable isn't Thunderbolt.

First-time setup

About five minutes, once.

Re5k is sold directly, not through the App Store, so macOS asks you to approve it the first time. After that it just opens.

1 · Allow it to open

Open the app once. When macOS says it can't verify it, go to System Settings → Privacy & Security, scroll down, and click Open Anyway. Do this on both Macs. On macOS 12, Control-click the app and choose Open.

2 · Turn on permissions

On your Mac: Screen Recording, Accessibility and System Audio Recording. On the iMac: Accessibility. The Setup Check window has a button for each one.

3 · Two settings

On both Macs, turn off Universal Control (Displays → Advanced). On the iMac, set Lock Screen → “Require password after display is turned off” to Never, so the iMac's login screen doesn't cover the picture when it wakes. On macOS 12, that's System Preferences → Security & Privacy → General.

Troubleshooting

Something not right?

First, make sure every light is green on both Macs. On your Mac, click the Re5k icon in the menu bar at the top of the screen and choose Setup Check…. On the iMac, the checklist shows on its screen whenever your Mac isn't connected. Any red light tells you what's wrong and has a button to fix it. If everything is green and something still isn't right, here are the most common problems.

“Re5k can't be opened” or “Apple could not verify”

This is expected the first time for apps sold outside the App Store. Go to System Settings → Privacy & Security, scroll to the bottom, click Open Anyway, and confirm with your password.

If there's no Open Anyway button, open Terminal and run this, then open the app again:

xattr -dr com.apple.quarantine /Applications/Re5k*

The menu bar says “Looking for your iMac” and never connects
  1. Make sure Re5k (iMac) is open on the iMac. It fills the screen while it waits.
  2. Check the cable link: System Settings → Network → Thunderbolt Bridge should say “Self-Assigned IP” on both Macs.
  3. Unplug the cable for five seconds and plug it back in. It sometimes takes two tries.
  4. Both Macs need the same Re5k version. After an update, reinstall on the iMac too.
  5. If macOS asked about Local Network access, click Allow on both Macs.
“Found your iMac on Wi-Fi, but not over the cable”

Both Macs can see each other, but the Thunderbolt link isn't up. Re5k won't stream over Wi-Fi. Usually the cable is a USB-C charging cable rather than Thunderbolt, or there's a hub in between. Swap in a Thunderbolt 3, 4 or 5 cable and connect it directly.

The iMac stays black, or the picture never appears

macOS only applies Screen Recording permission after the app restarts. Turn on Re5k (MacBook) in System Settings → Privacy & Security → Screen Recording, then click Relaunch in Setup Check.

If you just updated Re5k and permissions look on but nothing works, remove Re5k from the list with the − button and add it again.

The iMac's keyboard and mouse don't control my MacBook
  • Turn on Accessibility for Re5k on both Macs: System Settings → Privacy & Security → Accessibility.
  • Turn off Universal Control on both Macs. It fights Re5k for the keyboard and mouse.
  • Keep the keyboard and mouse paired to the iMac, not the MacBook.
No sound from the iMac

Sound needs macOS 14.2 or newer on your Mac, and permission for System Audio Recording (System Settings → Privacy & Security). Make sure Play Sound on iMac is checked in the Re5k menu.

The iMac shows its own login screen when it wakes

On the iMac, open System Settings → Lock Screen and set “Require password after screen saver begins or display is turned off” to Never.

My MacBook went to sleep and won't wake from the iMac

Keep the MacBook plugged into power while you use it closed. While connected, Re5k lets the screens sleep but keeps the Mac itself awake, so a keypress wakes both. If you choose Sleep from the Apple menu, the Mac fully sleeps: wake it with its own keyboard, or by opening the lid.

Video stutters or full-screen motion looks choppy

Re5k sends a lossless picture so text stays perfectly sharp. Busy full-screen video is the hardest case, especially on the 2017 iMac. Desktop work, browsing and documents are smooth. For movies, play them in a window or on the MacBook's own screen.

My printer, drive or cutter is plugged into the iMac and my Mac can't see it

That's expected. Re5k turns the iMac into a display with its keyboard, mouse and speakers. It isn't a USB hub, so other things plugged into the iMac still belong to the iMac.

  • USB printers: share them from the iMac. On the iMac, open System Settings → General → Sharing and turn on Printer Sharing. Then on your Mac, open System Settings → Printers & Scanners → Add Printer and pick the iMac's printer. It prints over your network, and the iMac is always on while Re5k runs.
  • Cutters, plotters, scanners, drives and other USB gear: plug them into your Mac instead. A small USB hub next to your Mac keeps it to one plug. Devices with a network (Ethernet) port can go on your network and be reached from your Mac directly.
  • Need the iMac for a job? Press Control Option Command Q on the iMac to use it as its own Mac, then reopen Re5k (iMac) when you're done.
How do I get back to the iMac's own desktop?

Press Control Option Command Q on the iMac's keyboard. When no Mac is connected, pressing Esc twice also works.

Can I use my 5K iMac as a monitor? Doesn't Target Display Mode do that?

Not on a 5K iMac. Apple's Target Display Mode only worked on older, non-Retina iMacs from 2009 to 2014, and no 27″ 5K iMac has ever supported it, whatever cable you use. Re5k does the same job in software: your MacBook sees a real 5K external monitor, and the iMac shows it over one Thunderbolt cable, along with its keyboard, mouse and speakers.

Can I use the iMac's camera or microphone on video calls?

Not yet. The iMac's camera and microphone stay with the iMac. For your MacBook's apps (FaceTime, Zoom, Teams) to see them, Re5k would need to add a virtual camera and microphone to the MacBook, and macOS only allows that for apps signed through Apple's paid developer program. Re5k skips that to keep the price low.

What works today: with the lid open, use the MacBook's own camera and mic. With the lid closed, use your iPhone as the camera with Continuity Camera (it appears in your video apps automatically), or plug a USB webcam into your MacBook. If Re5k grows enough to join Apple's program, camera and microphone support is first on the list.

Why does it ask for Screen Recording and Accessibility? Is it tracking me?

The apps have no tracking, no analytics, no ads and no accounts. Screen Recording lets the MacBook app read the picture of the one extra screen it shows on the iMac (not your MacBook's own screen) and send it over the cable. Accessibility lets the iMac's keyboard and mouse control your Mac. Everything goes live over the Thunderbolt cable between your two Macs and is never recorded, saved or uploaded.

The MacBook app only goes online to check for updates and to check your license key. The iMac app never goes online. Every detail is on the Privacy & Terms page.

How does the free trial and license work?

The download is the full app. It works for 7 days from the first time you open it on your Mac, with no card needed. Near the end, the MacBook app reminds you with a License window. On day 8, the iMac shows a "Your free trial has ended" screen instead of your Mac's picture. To keep using it, buy a license for $9.99. Your key arrives by email. On your Mac, click the Re5k icon in the menu bar, choose License…, paste the key and click Activate. The picture comes back right away. One key works on two of your Macs. Only the MacBook app needs it.

Moving to a new Mac? Open License… on the old one and click Remove License from This Mac, then activate it on the new one. Lost your key? Email support@re5k.app.

How do I uninstall Re5k?

Quit Re5k (Quit is in the menu bar icon on your Mac; on the iMac, press Control Option Command Q). Then drag each app from Applications to the Trash, and remove it from System Settings → General → Login Items.

Why I made this

My iMac deserved a second act.

I have a 2017 27″ iMac with a gorgeous 5K screen. The screen still looks amazing. The computer behind it just can't keep up anymore, and Apple stopped letting iMacs work as a monitor years ago.

My MacBook does the real work now, so the iMac mostly sat there. I tried a paid app to turn it into a display, but it kept glitching, and I was always re-pairing my keyboard and mouse between the two.

So I built Re5k for my own desk. One cable, the iMac's keyboard and mouse just work, and when I close my MacBook and tuck it away, the iMac sleeps and wakes right along with it. It's a small indie project, priced to be an easy yes. If it gives your iMac a second life too, that makes my day.

Eric · maker of Re5k

A 2017 27-inch iMac on a desk showing a MacBook's desktop, with the MacBook closed in a vertical stand beside it and the iMac's keyboard and mouse in front.
My desk: MacBook closed and docked, the 2017 iMac doing the work.
What to expect

It works. It isn't perfect.

Re5k is a pet project I built for my own desk and decided to share cheaply. It's what I use every day, and it does the job well. It's not a polished product from a big company, though, so here's the honest picture. Then try it free for 7 days and see for yourself.

Works well Everyday use

  • A sharp 5K picture for browsing, documents, design and code.
  • The iMac's keyboard, mouse and speakers controlling your Mac.
  • Sleeping and waking together, with the lid closed and the Mac on its charger.
  • Starting up on its own once it's set up.

A little fiddly The rough edges

  • One extra step to install. Re5k isn't notarized by Apple. That costs $99 a year, and I'd rather keep the price low. So macOS asks you to approve it once: System Settings → Privacy & Security → Open Anyway. After that, it opens like any other app.
  • About five minutes of setup: a few permissions on each Mac. The checklist walks you through it.
  • Fast motion like full-screen video or games can stutter, especially on older iMacs.
  • USB devices stay with the iMac. Printers can be shared; other gear plugs into your Mac.
  • The iMac's camera and microphone aren't passed through. For video calls, use your MacBook's own camera, your iPhone with Continuity Camera, or a USB webcam.
  • Now and then, a quick replug clears up a hiccup, like a stray pointer.

That's why there's a free trial instead of a refund: you get 7 days with everything working, on your own Macs, before you spend anything. Because you can try first, purchases are final. Stuck on something? Email support@re5k.app and I'll help.

Try free for 7 days, then one price
$9.99
  • Re5k for your Mac and for your iMac
  • One license key works on two of your Macs
  • Free updates for version 1
  • No account, no subscription, nothing to sign in to
Start your free 7-day trial Buy a license · $9.99
No card needed for the trial: enter your email and the download link arrives right away. After 7 days, the MacBook app asks for a license key. Buy one and the key arrives by email: paste it in from the menu bar (License…). Because you can try first, purchases are final.