Which way fits your iMac
- 2009 to mid 2014: Target Display Mode.
- Late 2014 and mid 2015 (Retina 5K): neither Target Display Mode nor Second Display. Luna Display lists Macs from 2011 on.
- Late 2015 and newer: Second Display, Duet Display or Luna Display.
- 2019 and newer, and the iMac Pro: also AirPlay to Mac.
Second Display: an app for iMacs from late 2015
An app on both Macs that makes the iMac an extra display of the Mac you work on. The iMac needs macOS 12.3 or later, the Mac you work on macOS 14 or later. Over a Thunderbolt cable the picture is exactly what your Mac draws, at 60 frames per second. Over Wi‑Fi, Ethernet or a USB‑C cable without Thunderbolt it is slightly softer. Which iMacs can be a display · Thunderbolt: which cable and which port?
In our test, a MacBook Pro with M3 Pro sent a moving picture to an iMac 24‑inch with M1 over Thunderbolt with a median delay of about 9 milliseconds. What “about 9 ms” means
Best for an iMac from late 2015 on: no dongle, one payment.
Target Display Mode: Apple’s own way, up to mid 2014
Started with Command‑F2 on the iMac. It works on 24-inch and 27-inch iMacs from 2009 and 2010 and on iMacs from 2011 to mid 2014, running macOS High Sierra 10.13.6 or earlier. The other Mac must be from 2019 or earlier, with macOS Catalina 10.15.8 or earlier, so a Mac with Apple silicon can’t use it. Apple: Use iMac as a display with target display mode
Best for an older iMac next to an older Mac. Target Display Mode and newer iMacs
AirPlay to Mac: streaming to a 2019 or newer iMac
Built into macOS Monterey and later. A Mac with AirPlay Receiver turned on shows what an iPhone, iPad or another Mac sends it, over the same Wi‑Fi network. Apple lists the iMac Pro and Macs introduced in 2018 or later. Apple: Continuity requirements
Best for a 2019 or newer iMac and wireless streaming of video, photos or a screen. iMac not showing in AirPlay to Mac
Luna Display: a dongle for the Mac you work on
Astropad’s Luna Display is a small dongle that plugs into the Mac you work on, with Astropad’s app on the second Mac. Astropad lists Macs from 2011 on with macOS 10.13 High Sierra or later. Astropad: Luna Display
Best for anyone who wants a dedicated dongle.
Duet Display: an app on both Macs
Duet connects wirelessly, or by Thunderbolt cable between two Macs on macOS 12.3 or later. Duet: Use an iMac as a monitor
Best for anyone who already uses Duet.
Sidecar: for an iPad, not an iMac
Sidecar makes an iPad a display for your Mac. It doesn’t work with a Mac as the display. Apple: Use an iPad as a second display
Side by side
| Method | Needs | Connection | Price |
|---|---|---|---|
| Second Display | iMac from late 2015, macOS 12.3 or later | Thunderbolt cable, Wi‑Fi, Ethernet or USB‑C | Free for 7 days, then $39 once |
| Target Display Mode | 24-inch and 27-inch 2009 and 2010; 2011 to mid 2014 | Thunderbolt or Mini DisplayPort cable | Built into macOS |
| AirPlay to Mac | iMac Pro and 2019 on, macOS Monterey or later | Wi‑Fi network | Built into macOS |
| Luna Display | Mac from 2011, macOS 10.13 or later | Dongle on the Mac you work on | $89.99 once, USB‑C version |
| Duet Display | macOS 12.3 or later on both Macs, for the cable | Wireless, or Thunderbolt cable | On Duet’s site |
As of October 2026, from each maker’s own pages.
More guides: use an old iMac as a monitor and an alternative to Target Display Mode.
Questions
How do I use my iMac as a monitor?
On an iMac from late 2015 on, install Second Display on both Macs and connect them with a Thunderbolt cable, Wi‑Fi or Ethernet. On an iMac from 2009 to mid 2014, use Apple’s Target Display Mode with an older Mac.
What is the best app to use an iMac as a second display?
Second Display, for an iMac from late 2015 on. It is an app on both Macs, and over a Thunderbolt cable the picture is exactly what your Mac draws, at 60 frames per second. It costs $39 once, with every future update.
Is there a Luna Display alternative without a dongle?
Yes: Second Display. It is an app on both Macs that needs no dongle. Connect them with a Thunderbolt cable, Wi‑Fi or Ethernet. It costs $39 once, and the 7-day free trial needs no payment details.
Can I use an iMac as a monitor for a Mac with Apple silicon?
Yes, with an app. Apple’s Target Display Mode needs the other Mac to be from 2019 or earlier, so it can’t work with an M1, M2 or M3 Mac. Second Display works with Apple silicon Macs on macOS 14 or later.
Can Sidecar use an iMac as the display?
No. Sidecar makes an iPad a display for your Mac. It doesn’t work with a Mac as the display.
Can I use an iMac as a monitor over Wi‑Fi?
Yes. AirPlay to Mac and Second Display both work over a Wi‑Fi network. With Second Display the picture is slightly softer over Wi‑Fi than over a Thunderbolt cable.