Need more screen space but don’t want to buy a dedicated monitor? If you have an extra laptop sitting around, you might wonder if you can use its screen as a second display for your main desktop or another laptop. It’s a clever way to repurpose existing hardware and boost your productivity. I’ve definitely used this trick when working remotely and needing that extra screen real estate.
The challenge is that the video ports on laptops (like HDMI or DisplayPort) are almost always outputs, designed to send video from the laptop, not receive it. You can’t just plug a cable from your main computer’s output into your laptop’s output and expect it to work. The solution involves using software to send the display signal over a network connection.
This guide will show you two main ways to use your Windows laptop as a second monitor for another computer using software, turning that extra screen into a useful display.
Why Can’t I Just Use a Cable? (The Input/Output Problem)
Most commonly, the HDMI, DisplayPort, or VGA ports on a laptop are designed to send video from the laptop’s graphics card to an external display. They are output ports. Standard monitors have video input ports. You need an output connecting to an input. Since a laptop’s video ports are typically outputs, you can’t directly plug your main computer’s video output cable into your laptop’s video port and have the laptop screen act as a monitor input. Software workarounds are needed to send the video signal over a network.
Method 1: Use Windows’ Built-in “Projecting to this PC” (No Extra Software)
Windows 10 and 11 have a feature that allows one Windows PC to wirelessly project its screen onto another Windows PC over your local network or using Wi-Fi Direct (Miracast). The laptop you want to use as the second monitor acts as the receiver.
Step 1a: Set Up the Laptop (The “Monitor”)
First, configure the laptop that you want to use as the second monitor to be available for projection.
- On the laptop you’ll use as the secondary display, click the Start button and open Settings.
- Click on System.
- Scroll down the left-hand menu and click on Projecting to this PC.
- Under “Some Windows and Android devices can project to this PC when you say it’s OK,” click the dropdown menus and choose when this PC should be available:
- “Available everywhere” or “Available on secure networks” (Choose one that suits your environment, secure networks is generally safer).
- “Ask to project to this PC” or “Always allow” (Select “Ask to project to this PC” is recommended for security).
- You can also choose to “Require PIN for pairing” for extra security. Toggle this On if desired.
- Note the PC name: Look under “Launch the Connect app to project to this PC.” It will show the name of the PC (e.g., “DESKTOP-ABCD”). You’ll need this name on the other computer.
Leave this laptop on and connected to your Wi-Fi network.
Step 1b: Connect from the Other Computer (The “Source”)
Now, on the computer whose display you want to extend, you will connect to the laptop.
- On the computer you want to project from, make sure it is connected to the same Wi-Fi network as the laptop (or connected via Ethernet to the same router).
- Press the Windows Key + P on your keyboard. This opens the “Project” sidebar.
- Click on Connect to a wireless display at the bottom of the sidebar.
- Windows will search for available wireless displays. Find the name of the laptop you set up in Step 1a (the name you noted down).
- Click on the laptop’s name in the list.
Step 1c: Authorize the Connection (On the Laptop)
Go back to the laptop you’re using as the monitor.
- A notification should appear asking if you want to allow the other computer to project. Click Yes or Allow.
- If you enabled the PIN option, you will also need to enter the PIN shown on the laptop’s screen onto the source computer.
Step 1d: Configure Display Mode (On the Other Computer)
Once authorized, the laptop screen will become active as a connected display.
- Go back to the computer you are projecting from. Press Windows Key + P again.
- Choose how you want to use the laptop screen:
- Extend: This uses the laptop screen as a second, separate desktop area. (Most common for using it as a second monitor).
- Duplicate: This mirrors your main screen onto the laptop screen.
- You can further adjust the resolution and arrangement of this new display in Settings > System > Display on the source computer, just like with a physically connected monitor.
Method 2: Use Third-Party Software (Often More Flexible)
Several third-party applications allow you to use a laptop (or tablet/phone) screen as an extra monitor over your network. These can sometimes offer better performance or features than the built-in option. A popular free option for personal use is SpaceDesk.
Step 2a: Download and Install SpaceDesk SERVER (On the “Source” Computer)
You need server software on the computer whose display you want to extend.
- On the computer you want to project from (your main PC), go to the official SpaceDesk website: spacedesk.net.
- Go to the Download section.
- Download the SpaceDesk DRIVER software for Windows Primary Machine (server) that matches your Windows version (Windows 10 or 11, 32-bit or 64-bit).
- Run the downloaded installer file and follow the on-screen instructions to install the server software.
Step 2b: Download and Install SpaceDesk VIEWER (On the Laptop “Monitor”)
You need viewer software on the laptop that will act as the display.
- On the laptop you want to use as the second monitor, go to the same SpaceDesk website: spacedesk.net.
- Go to the Download section.
- Download the SpaceDesk VIEWER application. There are viewers for Windows, Android, and iOS. Download the Windows VIEWER for your laptop.
- Run the downloaded installer file and follow the on-screen instructions to install the viewer software on your laptop.
Step 2c: Connect Both Devices Using SpaceDesk
Make sure both computers are on the same network.
- Ensure both the main computer and the laptop are connected to the same Wi-Fi network or both connected via Ethernet to the same router.
- On the main computer (the source), launch the SpaceDesk DRIVER Console application. Ensure the “SpaceDesk service” is running (it usually starts automatically). It will show you the network adapter it’s using.
- On the laptop (the monitor), launch the SpaceDesk VIEWER application.
- The Viewer should automatically detect the SpaceDesk server running on your main computer on the same network. You will see the main computer’s name or IP address listed.
- Click on the main computer’s name or IP address in the SpaceDesk Viewer app to initiate the connection.
Step 2d: Configure Display Mode in Windows
Once connected via SpaceDesk, your laptop’s screen will be recognized by the main computer as another display.
- On the main computer (the source), press Windows Key + P.
- Select Extend or Duplicate.
- You can further arrange the displays and adjust resolution/scaling in Settings > System > Display.
Troubleshooting Common Issues
- Laptop Not Appearing (Built-in Method):
- Ensure both PCs are on the same network.
- Verify “Projecting to this PC” settings are enabled correctly on the laptop (available everywhere/on secure networks, allow connections).
- Restart both computers and your router.
- Check Windows Firewall on both PCs to ensure communication isn’t blocked.
- Make sure the source PC supports Miracast (most modern ones do).
- SpaceDesk Not Connecting:
- Verify both computers are on the exact same network (check IP addresses to be sure).
- Ensure the SpaceDesk SERVER is running on the main PC and the VIEWER is running on the laptop.
- Check Windows Firewall on both PCs to ensure it’s not blocking SpaceDesk. You might need to add exceptions.
- Try restarting both the SpaceDesk service/app and then both computers.
- Significant Lag, Choppiness, or Delay: This is the most common issue with network-based display solutions over Wi-Fi.
- Improve Network Connection: This is the best fix for lag. If possible, connect one or both computers to your router using an Ethernet cable. Ideally, connect both to the router or directly connect them with an Ethernet cable (might require specific setup). A strong, less congested 5GHz Wi-Fi band is usually better than 2.4GHz.
- Lower Resolution: On the source computer, in Display settings, lower the resolution of the laptop’s display. This sends less data over the network.
- Check Resource Usage: Open Task Manager on both computers (Ctrl+Shift+Esc). See if either machine’s CPU, Memory, or Network usage is maxed out, which can cause delays.
- Firewall Blocking: Ensure your firewall (Windows Firewall or third-party) allows the specific network traffic or the SpaceDesk applications through on both computers.
- Display Settings Won’t Apply: After connecting via software, if Windows display settings are acting strange, try disconnecting the software connection, verifying Windows recognizes only the main screen, then reconnecting with the software and trying display settings again.
Limitations of Using a Laptop as a Monitor
Using a laptop screen as a second monitor via software isn’t the same as a direct cable connection:
- Latency: There will almost always be some delay or lag compared to a wired monitor, especially over Wi-Fi. This might be fine for static windows but noticeable for fast-paced video or gaming.
- Performance Impact: It uses resources (CPU, Network) on both the source computer and the laptop being used as the display.
- Battery Drain: Using a laptop this way will drain its battery unless it’s plugged in.
- Resolution/Refresh Rate: You might be limited to lower resolutions or refresh rates compared to the laptop’s native capabilities or a wired connection.
Despite these limitations, using a laptop screen as a second monitor via built-in Windows features or free third-party software like SpaceDesk is a practical and free way to get extra screen space using hardware you already own. It takes a few steps to set up, but having that extra display available can significantly boost your workflow.