Two monitors are better than one, and with a Mac running macOS Catalina or later, you can turn your iPad into a second display with Sidecar, which allows your computer to talk with your tablet and extend the same desktop environment.

However, this feature is limited to only certain Mac and iPad models, which is a bummer if you have an older device or a Windows PC. Thankfully, a few third-party apps can help fill the void on all the devices that can't run Sidecar.

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Sidecar is arguably the best option for turning your iPad into a second display. So if you have a Mac and an iPad from the past five or six years, you'll want to try this method first. (If your devices are older than that, skip down to the next section.)

To connect your iPad as a display, either connect your iPad to your Mac over USB, or ensure Bluetooth, Wi-Fi, and Handoff are turned on to do it wirelessly. You'll also need to be logged in to the same Apple ID on both devices.

Click the AirPlay button in your Mac's menu bar and select your iPad from the list. The icon will change, and clicking the menu again will offer you a number of options. You can extend or mirror your Mac's display, show or hide the Sidebar and Touch Bar that appear on the iPad, or disconnect your tablet.

If you want to switch between a wired and wireless connection, you will have to disconnect and re-connect using the AirPlay menu. Apple says it should work wirelessly as long as the iPad is within 10 meters (30 feet) of the Mac, and you can even use your Apple Pencil to sign documents and draw in supported apps.

If your Mac or iPad isn't supported by Sidecar—or you're a Windows and Android user—Splashtop Wired XDisplay is a third-party app that can turn your tablet into a second monitor. It only works when connected over USB, and isn't the smoothest option I've used, but it will do the job adequately for not a lot of money.

Splashtop Wired XDisplay has two components: A desktop agent that runs in the background on your PC or Mac, and an app for iPadOS or Android that runs on your tablet. (The iPad app appears to be free, while the Android app is $7 — though there's a free trial version that works for 10 minutes at a time.)

Install the desktop app and mobile app on the devices you wish to use together. With the desktop app running, connect your tablet to your computer with a USB cable, then launch the XDisplay app on your tablet. It will establish a connection to your computer, and a blank desktop will appear on your tablet.

You can rearrange your monitors from your computer's Display settings, drag windows to your tablet, and otherwise use it as a second monitor for a productivity boost. I recommend having a stand to keep it propped up — something like this works great if you're using your tablet with a laptop, while a more adjustable stand is ideal for desktop usage.

Splashtop Wired XDisplay works decently well, at least in my experience using an iPad and a Windows PC. There is some noticeable latency, and I did have some trouble with it getting stuck in Mirrored Mode on one of my computers, but for the price of free, it's worth a shot. (The $7 Android app has more mixed reviews, and if you're going to pay money, I think it's worth shelling out a few more and using our paid recommendation, Duet Display, below.)

If you want the smoothest experience possible, Duet Display is the best app I've tested for turning an iPad into a second monitor. Like Splashtop, it has an app for your tablet that connects to a companion app on your computer. You're free to test out the service for 10 minutes at a time, but for longer usage (or additional features like wireless connections) you will need to subscribe to a tiered pricing plan(Opens in a new window).

Sign up for an account, then install the desktop and tablet apps. With the desktop app running in the background on your PC. Plug your tablet in via USB and launch the Duet Display mobile app. If you pay for the $24.99 per year Duet Air plan, make sure to sign in to wirelessly connect your devices. You must then enable screen sharing in Duet settings. Select the computer under the Air tab in the app to connect.

Finally, click the Duet Display icon on your PC to gain access to a few other settings, like the frame rate and resolution your tablet uses. For me, the default settings worked great, but if you find it's being a bit sluggish on an older laptop, lowering the resolution, frame rate, or power usage from this window may help.

Duet Display may be more expensive than its competitors, but in my experience, it's been the smoothest experience by far. If you use your iPad as a second monitor regularly, it's well worth the price.

This article originally appeared on PCMag.com, Mashable's sibling site. PCMag.com is a leading authority on technology, delivering Labs-based, independent reviews of the latest products and services.