Every way to use an old iMac as a monitor, compared

If your main Mac is from 2020 or later, Apple's Target Display Mode is out, so the realistic ways to use an old Intel iMac as a monitor are an app (free Encore, or paid RetinaRelay, MacDisplay, Luna Display or Duet), AirPlay to Mac if the iMac is from 2019 or later, or hardware (a capture card or a display driver board). Which one fits depends on the iMac's year, whether you want native 5K, and what you want to pay.

The quick decision

• Your iMac is from 2009 to 2012: Encore (free, Late 2009 and up, 2007 to Early 2009 with the Legacy receiver) or Luna Display (from 2011, with a dongle). The new paid apps start later.
• You have a 27-inch 5K iMac and want native 5K: RetinaRelay or Luna Display claim it. Encore sends Retina iMacs at up to 2560 × 1440 today.
• You want a measured latency figure before you choose: Luna Display and MacDisplay publish numbers from their own tests. Encore has not published one yet.
• Your main computer is a PC, or you also want an iPad: Luna Display or Duet.
• You want it free, with the iMac's keyboard, mouse and speakers working for your Mac: Encore.
• Your iMac is from 2019 or 2020 and you only need it now and then: AirPlay to Mac is built in.
• You never need the iMac as a computer again: a driver board turns a 27-inch 2014–2020 panel into a plain monitor.

The table

Prices and requirements as listed by each maker on 1 November 2026. "Oldest iMac" is the oldest model the maker's own requirements allow.

Apple's built-in options

Target Display Mode is the cleanest picture of all, a real monitor over a cable, but it only works with a Mac introduced in 2019 or earlier on macOS Catalina or older, per Apple's support page. We explain the rules in Target Display Mode explained.

AirPlay to Mac needs an iMac from 2019 or later on macOS 12 Monterey or later (TidBITS). It is built in and free. MacMost calls it "slower and less responsive" than a cable for everyday second-screen work.

Sidecar is for an iPad, not a Mac. Universal Control shares a keyboard and mouse between Macs but not a screen, and Apple lists iMacs from 2017 and the 5K Late 2015 (Apple). Screen Sharing mirrors the other Mac rather than extending your desktop.

Apps

Encore is ours. It is free during early access, with no account and no dongle, and it reaches the oldest iMacs: every Intel iMac from Late 2009 to 2020 on macOS 10.13 or later, and 2007 to Early 2009 with Encore Receiver Legacy. It works over Wi‑Fi, Gigabit Ethernet or Thunderbolt. The iMac's own keyboard and mouse can control your Mac, your Mac's sound can play on one or more iMacs at once, and when the iMac isn't a screen it can show a StandBy clock with weather and your calendar.

Where Encore is weaker, plainly:

• No published latency yet. Our figures are design targets until we publish measurements per iMac model.
• Retina iMacs are encoded at up to 2560 × 1440, not native 5K.
• It needs macOS 14 or later on your Mac. RetinaRelay accepts 13, MacDisplay 12.3, Luna and Duet 10.13.
• It is not notarized by Apple, so macOS shows a warning once; the install guide shows the clicks.
• It is an early beta, and the picture is still being checked model by model.

Luna Display by Astropad is a small hardware dongle that plugs into your main Mac. Astropad lists it at $89.99, from $59.99, supports iMacs from 2011, and needs macOS 10.13 on both Macs with a USB-C port on the main one (requirements). It can do native 5K with the USB-C unit, works with PC hosts too, and Astropad published a latency test of about 22 ms. Pick it if you want native 5K on a 2011-or-later iMac and don't mind the dongle.

Duet sells subscriptions: Air at $49.99 a year and Pro at $79.99 a year (App Store prices). It has a page for exactly this job and also covers iPads, Android and PCs. Thunderbolt needs macOS 12.3 or later on both Macs.

RetinaRelay launched in October 2026: $49 once, one host Mac and unlimited iMacs, a 7-day trial. The host needs macOS 13 or later and the iMac must be Late 2012 or later on macOS 10.15 or later. It is built for cables and claims native 5K at 60 fps. MacGeneration covered it. Pick it if you have a 5K iMac and a cable, and want native resolution.

MacDisplay costs €29.99 plus VAT, once, for three Macs, with a free tier limited to 10-minute sessions and 60 minutes a day. The receiving iMac needs macOS 11 or later, which means 2014 or later. It is notarized, and its own photographed Ethernet tests show about 70–80 ms.

Two more exist: Yam Air Desk ($7.99 after a trial, receiving Mac on macOS 10.15 or later) and Spantop, which needs macOS 14 on Apple silicon and so doesn't run on an Intel iMac.

Hardware

A capture card (about $20) with an HDMI viewer app turns the iMac into a window onto any HDMI source, but the iMac needs macOS 14 or later, so in practice a 2019 or 2020 model (9to5Mac).

A display driver board replaces the computer inside a 27-inch 2014–2020 iMac so the panel becomes a plain 5K monitor. Kits cost about $265–300, and the iMac stops being a computer: no macOS, no camera, no speakers.

Keeping the iMac's own system alive

OpenCore Legacy Patcher installs newer macOS versions on unsupported Macs, which can bring AirPlay to Mac to a 2012–2015 iMac. It works for many people, but it patches the operating system and comes with model-specific limits.

How we keep this fair

We list where others are better, link every number to its source, and date the prices. If something here is wrong or out of date, tell us and we will fix it. To check your own model first, see the year-by-year guide or the compatibility page.