How to Use a Notebook as a Monitor (Extended Display or Second Screen)

Using a laptop as a secondary monitor sounds like a smart way to repurpose existing hardware — and in many cases, it genuinely is. But whether it works smoothly, works at all, or requires workarounds depends heavily on your operating system, hardware generation, and how you define "using it as a monitor."

Here's what's actually happening under the hood, and what shapes the experience.

What "Using a Notebook as a Monitor" Actually Means

There are two distinct scenarios most people are describing when they ask this:

1. Extending or mirroring a desktop or another laptop's display onto your notebook screen
2. Using the notebook as a physical monitor by connecting a second device's video output directly into it

These sound similar but are technically very different — and the second one is where most people hit a wall.

Why You Can't Just Plug In an HDMI Cable

Most laptops have HDMI-out only, not HDMI-in. The port is designed to send video signal to an external display, not receive one. Plugging a second computer into your laptop's HDMI port won't work — there's no hardware path for incoming video on standard consumer notebooks.

A laptop would need a capture card input, a Thunderbolt port with DisplayPort Alt Mode in target display mode, or a manufacturer-specific feature to accept external video. These exist, but they're not common on mainstream laptops.

Method 1: Software-Based Display Extension (Most Common Approach)

This is how the majority of users actually accomplish the goal — using software to extend a Windows PC or Mac's desktop wirelessly (or over a local network) onto a second laptop's screen.

Windows: Miracast and the "Project to This PC" Feature

Windows 10 and Windows 11 include a built-in feature under Settings → System → Projecting to this PC. When enabled, the receiving laptop appears as a wireless display target on other Windows devices.

Requirements:

• Both devices must support Miracast (most Intel/AMD laptops from ~2015 onward do)
• Both on the same Wi-Fi network, or Wi-Fi Direct capable
• Windows 10/11 on the receiving device

To connect from the source machine: press Win + K to open the Cast panel and select the receiving laptop.

What works well: Quick setup, no cables, decent for productivity tasks like reference documents or dashboards.

What degrades the experience: Wireless latency makes it unsuitable for video editing previews or anything requiring frame-accurate display. Resolution and refresh rate are also capped by the Miracast implementation.

macOS: Sidecar (iPad) and Third-Party Apps for Laptops

Apple's Sidecar feature extends a Mac's display to an iPad — not to another Mac. If you're trying to extend one Mac onto another Mac's screen, you'll need third-party software like Luna Display (which uses a hardware dongle) or apps like Deskreen or Space Desk (Windows-side alternatives).

These tools create a virtual display driver on the source machine and stream it to the receiver over a local network.

Method 2: Hardware-Based Input (Capture Cards and Thunderbolt)

For users who need the notebook screen to display input from a gaming console, camera, or another PC with an actual video output signal, a USB capture card is the functional solution.

A capture card connects via USB to the laptop and presents itself as a webcam/video input device. You view the incoming signal through software like OBS, VLC, or a dedicated capture app. This works — but it's not a true monitor replacement. There's inherent encoding latency, and resolution/framerate depend on the capture card's specs and USB bandwidth.

Thunderbolt Target Display Mode

Some older Apple MacBooks supported Target Display Mode, turning a MacBook into a monitor for another Mac via Thunderbolt or Mini DisplayPort. Apple discontinued this feature after 2014 iMacs, and it was never a widespread laptop feature even during its era.

No current mainstream Windows laptop supports an equivalent native feature.

Key Variables That Determine Your Setup 🖥️

Latency, Resolution, and Real-World Limitations

Software-based wireless methods introduce latency ranging from roughly 30ms to over 150ms depending on hardware and network conditions. For static reference content — a spreadsheet, documentation, a chat window — this is rarely noticeable. For video playback or fast-moving interfaces, it becomes disruptive.

Resolution is typically capped at 1080p for most wireless implementations, even if both screens support higher. Refresh rate is similarly constrained, often sitting at 30–60Hz regardless of display capability.

Wired approaches via capture card or purpose-built software like Luna Display (which uses a proprietary USB-C/Lightning dongle) reduce latency meaningfully but add hardware cost and setup complexity.

How Different Users End Up in Different Places 🔧

A user with two modern Windows laptops on a strong Wi-Fi 6 network enabling Miracast gets a usable, cable-free second screen in under five minutes. A user trying to connect a PS5 to a laptop screen needs a capture card and display software. Someone on older hardware may find Miracast unsupported or unreliable and end up routing through a third-party streaming app instead.

The method that makes sense depends on what device is sending the signal, what laptop is receiving it, what OS each is running, and what you're actually trying to display — factors that vary enough from one setup to the next that the same answer doesn't apply across the board.