You'd like a secondary screen to increase your productivity in Windows 10, but you don't have another monitor handy. If you have a recent Windows laptop or tablet, though, you can use it as a wireless monitor.

What You'll Need

In order to take advantage of this trick, you'll need two Windows 10 machines that support the Miracast streaming video standard. Most newer laptops and tablets have this built in, as do some desktops. However, if you've built your own desktop, or have one that doesn't have a Wi-Fi adapter, it might not support Miracast. To make this work, you'll need to connect both machines on the same local Wi-Fi network.

If you're not sure whether or not your Windows laptop or tablet supports Miracast, click the Start button, type "Projecting" into the search box, and then click the "Projecting to this PC" result. If the settings menu says "This device doesn't support receiving Miracast," then you won't be able to use it as a wireless monitor.

Step One: Set Up The Receiving PC

Before you connect your two Windows machines, you'll need to enable the connection. On the PC you want to use as a wireless monitor (which we'll call the "receiving PC" for this guide), click the Start button, type "Projecting to this PC" into the search box, and then click the "Projecting to this PC" result.

This takes you to a Settings window. On the first drop-down menu, you need to select "Available everywhere" or "Available everywhere on secure networks." The second option means strangers won't be able to accidentally project their screen to yours on a public Wi-Fi network.

On the second drop-down menu, you can control whether Windows notifies you every time a device tries to project to this PC, or only the first time a new device connects. Choose "First time only" if you'll be using this machine as a monitor frequently.

Turn on the "Require PIN for pairing" option if you're using the machine in a crowded or insecure space. And the final option lets you prevent projection from happening when the laptop is not plugged in. Monitor projection can be very battery-consuming.

Make a note of the PC Name at the bottom of the screen. (It's "Defiant" in the screenshot above.) Now switch to the main PC---the one you want to use as the host for the wireless monitor.

Step Two: Establish The Connection

With your receiving PC ready, you can now project your screen from the main computer.

On your keyboard, press Windows+P to open the Project menu. On a touchscreen, slide your finger in from the left, and then tap ""Project" at the bottom of the Action Center menu instead.

On the Project menu, click or tap the "Connect to a wireless display" link.

After a moment, the receiver machine you set up in Step One will appear in the list. Click it.

The receiver machine will display a screen that says "[Host] is about to connect." (If you've set up a PIN or a permission request in Step One, you'll need to verify the connection here.)

By default on the first connection, your secondary machine will merely mirror what's on your primary PC's screen. To tweak this and use the secondary PC as a full extended monitor, proceed to Step Three.

Step Three: Adjust Your Monitor

Click the Start button on your main PC, type "Change display settings" into the search box, and then select the "Change Display Settings" result.

On this menu you can treat your receiver PC as any standard monitor. For ideal use of the screen, open up the "Multiple Displays" dropdown menu, and then choose the "Extend these displays" option. Click "Keep changes" on the warning that appears.

Now your desktop space is expanded across the screens of both your primary PC and your receiver PC. You can run programs over on the second screen and the main screen at the same time, or extend a single program window across both of them.

By default the receiver PC screen will be positioned to the right of the main PC. If this doesn't match the physical configuration of your screens, you can click and drag the screens around at the top of this menu, and then click the "Apply" button.

And of course, your receiver PC is still running its own instance of Windows underneath the projected desktop. You can reach it by pressing Alt+Tab or sliding your finger in from the left edge of the touchscreen. The projected monitor from the main PC is a window labelled "Connect."

You won't be able to use the mouse, keyboard or touchscreen on the receiver PC to control the main PC unless you open the Action Center (Windows+A or slide your finger in from the right) and click the "Allow Input" notification. If you do, you won't be able to reach Windows "under" the projected monitor.

To stop using your receiver PC as a wireless monitor, press Windows+P or slide the Action Center open and tap "Project." Click or tap "Disconnect" at the top of the menu. Your wireless monitor will also stop working if the receiver PC shuts down.