Got an old laptop gathering dust? Before you recycle it, consider this brilliant hack: transform its screen into a fully functional secondary monitor. This practical repurposing expands your workspace without the cost of new hardware, potentially saving you money. Whether you’re a multitasker, a remote worker, or a creative professional, this guide shows you reliable methods to set it up. I’ll share tools, performance data, and my experience with this hack that transformed my home office.
For a related direction and endpoint-compatibility check, see USB-A Connector Guide: Roles, Data and Legacy Use.
Understanding the Approach
At its core, using a laptop as a monitor involves redirecting the video signal from your primary machine—whether it’s a desktop or another laptop—to the built-in display of your secondary laptop. This is different from connecting an external monitor to your laptop’s video output. Here, the secondary laptop *becomes* the monitor, receiving a signal from an external source.
This technique, known as laptop screen repurposing, is a sustainable way to create a portable secondary display using hardware you already own. If an older laptop is still functional, repurposing it can extend useful life, but verify software support, latency, power draw, security updates and the intended workload.
In my workflow, I dedicated an old laptop to Slack and Microsoft Teams, keeping these conversations visible without cluttering my main workspace. It minimized context-switching and helped maintain focus. Pro Tip: Before proceeding, check your laptop’s screen for dead pixels or backlight issues. A quick test using solid white, black, and red images will help you spot any potential display problems.
Software vs. Hardware Solutions
Software-Based Screen Sharing
The first and most accessible option involves using specialized software. Apps like Spacedesk or Input Director allow you to install a virtual display driver on your main PC and a viewer on your secondary laptop. Both devices communicate over your local network.
Advantages: This method is highly flexible. It requires no cables and works well for temporary setups or even using a tablet as a secondary display.
Challenges: The performance is reliant on your network connection. Over a crowded Wi-Fi network, expect input lag or visual artifacts. For static content, like reading documents, it works well. But for dynamic tasks like dragging windows or full-screen video, performance can be sluggish. Quick Tip: If you experience lag, try disabling antivirus software or firewall temporarily to test if it’s limiting the connection.
Hardware-Based Screen Sharing
Alternatively, a direct physical connection can offer better performance. However, most laptops only feature output ports, so a workaround is needed.
If you have a rare laptop with an HDMI-in port, such as older Lenovo ThinkPads or Alienware models, you’re in luck. Simply use an HDMI cable for a low-latency connection. If your laptop doesn’t have this port, you’ll need a USB video capture card. This device converts HDMI signals from your main PC into a USB stream that the secondary laptop can process.
Advantages: This method offers low latency (often under 30ms) and a consistent, uncompressed image, making it ideal for color-sensitive tasks or gaming.
Challenges: It requires additional hardware, which can add cost and setup time. Basic capture cards start at around $25, while high-end 4K models may exceed $150. But for those who already own a capture card, this is a cost-effective solution. Tip: When choosing a capture card, ensure it supports the resolution and refresh rate of your main PC to avoid bottlenecks.
Step-by-Step Guide to Using Your Laptop as an External Display
Now that you understand the two approaches, let’s dive into the step-by-step guide for setting up your laptop as a secondary display.
Depending on your needs, you can choose either the software or hardware method. Developers often use extra screens for documentation, while financial analysts rely on secondary displays to stream real-time market data. In my case, an old MacBook Air now hosts my music player, calendar, and task manager, reducing clutter and boosting productivity.
Method 1: Software-Based Screen Sharing
Step 2: Set Up the Network Both devices must be on the same local network. For the best performance, use a wired Ethernet connection for at least one of them. This provides a more stable connection than Wi-Fi. If you must use Wi-Fi, try positioning your router closer to improve the signal.
Step 3: Connect and Configure Open the server on your primary PC and the viewer on your secondary laptop. The viewer should detect the primary PC. Select “Extend these displays” in the Display Settings of your main computer. Adjust the resolution to match the native resolution of your laptop’s screen. For smoother performance, lower the color depth to 16-bit and the frame rate to 30 FPS in the Spacedesk server settings if you encounter lag.
Apple Ecosystem Alternative: If you’re using a Mac, “Duet Display” is a great alternative. It’s optimized for Apple products and offers a polished, low-latency experience.
Method 2: Direct Cable Connection
Scenario B: Using a Capture Card
- Get the Necessary Gear: You’ll need a capture card (e.g., Elgato Cam Link 4K) and an HDMI cable.
- Connect the Devices: Connect an HDMI cable from your main PC’s output to the capture card’s “HDMI In” port. Then, connect the capture card’s USB output to your laptop using a USB 3.0 port for the best performance.
- Display the Output: Open OBS Studio and add the capture card as a Video Capture Device. Right-click the preview window and select “Fullscreen Projector (Preview)” to display it on your laptop.
Important: Mouse movement between the screens isn’t handled by the OS’s native display settings. To seamlessly move the cursor, consider additional software like “Barrier” (free) or “ShareMouse” (paid). Expect minor latency (5-15ms).
Common Misconceptions and Limitations
Many people mistakenly assume that an HDMI cable between two laptops will allow them to extend their display. In reality, most laptop ports are *outputs*, not inputs. Plugging an output into another output results in a blank screen.
To establish a true direct connection, a laptop must have a video *input* port. If not, a capture card is your best option.
Performance limitations also exist. Software solutions typically max out at 60Hz, which may be insufficient for competitive gaming. Software-display performance varies by network, codec, host load and application. Test latency, motion and color behavior on the exact setup before relying on it. Test for yourself by moving video player windows across both screens—if it stutters, the setup may not meet your needs.
Optimizing Your Setup for Productivity
2. Improve Network Performance. If you’re using software-based solutions, dedicate a 5 GHz Wi-Fi band to your devices. It will reduce interference and improve network performance. Alternatively, create a mobile hotspot from your primary PC for a direct connection, bypassing the router.
3. Invest in High-Quality Cables. Use certified HDMI cables to avoid signal degradation and visual issues. Low-quality cables can make a 4K signal look blurry or cause dropouts.
4. Calibrate Your Displays. To reduce eye strain, ensure that your old laptop’s display matches the brightness and color levels of your primary monitor. Use tools like Windows’ built-in calibration wizard or DisplayCAL for more precise calibration.
5. Adjust Power Settings. To prevent your secondary laptop from going to sleep and interrupting your workflow, set it to never turn off the display or sleep while plugged in. Also, set the “Lid close action” to “Do nothing” so the laptop doesn’t automatically sleep when you close the lid.