Compare
Which option is actually right for you.
There are seven realistic ways to put a second screen next to your Mac. Most of the confusion comes from comparing them on price when the real question is what you are willing to trade.
The one question that decides it
Are you willing to use a cable?
If no, you are choosing between wireless options, and every one of them compresses the picture — squeezes it down to fit a link that is one to two orders of magnitude too narrow, then rebuilds an approximation at the other end. That is not a quality-of-implementation problem, it is arithmetic: a full 5K picture at 60 frames per second is about 10.6 Gbit/s, and Wi-Fi is nowhere near it. You will see it on small text and during motion.
If yes, the cable carries the whole picture and the compromise disappears. That is the trade DisplayBridge makes, and it is the reason it will never be wireless.
Side by side
| Option | What it needs | The picture | Cost |
|---|---|---|---|
| Target Display Mode | An iMac from 2009–2014, macOS Mojave or older | Native — it was a hardware input | Free, but discontinued |
| Sidecar | An iPad, not a Mac | Compressed | Free, built into macOS |
| AirPlay to Mac | Wi-Fi, macOS 12+ on the receiving Mac | Compressed, wireless latency | Free, built into macOS |
| Luna Display | A hardware dongle in one Mac | Compressed | ~$130 hardware |
| Duet Display | An account, on both machines | Compressed | Subscription, from ~$25/yr |
| Deskreen | A browser on the second machine | Compressed, browser-grade | Free, open source |
| DisplayBridge | A Thunderbolt cable, macOS 13+ on both | Uncompressed, up to full 5K at 60 Hz | $29 once, second Mac free |
Prices and capabilities checked 2026-09-06. Vendors change both — follow the links below before you buy anything.
The options in detail
Target Display Mode — the thing everybody is actually looking for
Apple's own feature, and the reason this whole category exists. Certain iMacs from 2009 to 2014 could accept a video input over Mini DisplayPort or Thunderbolt 2 and act as a plain monitor. It was perfect, it was free, and it is gone: Apple removed it in macOS Catalina in 2019, and the Retina 5K iMacs from 2017 onward never had it in the first place.
If you own a 2017 iMac, an iMac Pro, a 2019 or a 2020 iMac, there has never been a hardware way to do this. That gap is what every option below is trying to fill.
Sidecar — the one people confuse this with
Sidecar turns an iPad into a second screen for a Mac. It cannot turn a Mac into a screen for another Mac, which is what you are here for. If you have a spare iPad rather than a spare Mac, Sidecar is free, built in, and you should use it. Apple's documentation.
AirPlay to Mac — free, and you already have it
macOS 12 and later let a Mac act as an AirPlay receiver, so you can send a display to it over Wi-Fi with nothing to install. It costs nothing and it is worth ten minutes of your time to try before you consider paying anyone, including us.
What you will find: it is a compressed wireless stream. Text is softer than native, motion smears, and the lag is noticeable if you are typing or dragging. For a reference window or a video it is genuinely fine. For a screen you work on all day it is not.
Luna Display — the hardware answer
A small dongle you plug into one Mac, plus software on both. Mac-to-Mac mode arrived in version 4.0 in 2019, and later versions added Thunderbolt and Ethernet connections rather than only Wi-Fi. It is a well-regarded, long-maintained product from Astropad.
Two things to weigh: it is roughly $130 of hardware you have to buy and not lose, and the stream is still compressed — the dongle makes the connection reliable, not lossless. lunadisplay.com.
Duet Display — the subscription
Cross-platform and mature — iPad, Android, Windows and Mac, wired or wireless — built by ex-Apple engineers. If you want one tool that covers several kinds of second screen, it is the broadest option here.
It is a subscription, from around $25 a year on the individual tier, and it requires an account on both machines. The picture is compressed. duetdisplay.com.
Deskreen — free and open source
Sends your screen to any device with a browser, over the network. Zero cost, no account, works with anything that can load a web page. It is built on browser video streaming, so the picture quality and latency are what that implies — closer to a demo or a quick share than to a display you work on. deskreen.com.
BetterDisplay — worth naming, but not the same thing
Frequently recommended in the same threads, and often the right answer to a nearby question: it manages resolutions, HiDPI modes, brightness and dummy displays on the screens you already have. It is an excellent utility and it is not a way to send one Mac's desktop to another. BetterDisplay.
DisplayBridge
One app on both Macs, one Thunderbolt cable, click Connect. Because the cable is wide enough to carry the whole picture, nothing is thrown away: the full 5120 × 2880 at 60 Hz on a Retina 5K iMac, 120 Hz on a ProMotion MacBook Pro, 20–40 ms end to end. $29 once, three of your Macs, and the Mac acting as the screen is free forever.
Seven-day trial, no account, no sign-up, nothing leaves the cable. How it works · Setup guide.
When DisplayBridge is the wrong choice
Genuinely, buy something else if:
- You will not run a cable. This is not a preference we can design around — see the arithmetic at the top. AirPlay is free and already on your Mac; start there.
- Your second screen is an iPad. Use Sidecar.
- Either Mac is older than macOS 13 Ventura, or has no Thunderbolt 3 port.
- You want to control the other Mac from its own keyboard and mouse. That is remote desktop, not a display, and we do not do it.
- You need Windows on one end. This is Mac to Mac only. Duet or Deskreen cover that.
And if your iMac is from 2009 to 2014 and still runs macOS Mojave — use Target Display Mode. It is free, it is native, and it is better than anything on this page.
The short answer
Luna Display: $130 of hardware, compressed. AirPlay: free, blurry. DisplayBridge: pixel-perfect 5K at 60 Hz over the cable you already own — $29, and the second Mac never needs a license.