I have a drawer with three retired phones in it. For years they just sat there, batteries slowly dying, waiting for me to remember to recycle them. Then a reader emailed asking if there was any point keeping an old Android around besides "backup phone," and it made me actually try turning one into a second display for my laptop. I expected a gimmick. What I got was a genuinely useful extra screen that lives on my desk now, permanently propped up next to my main monitor.
This isn't new technology. Apps that turn a phone or tablet into a second screen have existed for years. What's changed is that the good ones got fast enough, and cheap enough, that the lag and setup hassle that used to make this not worth it mostly aren't a problem anymore — if you pick the right app and connection method.
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Why bother when you could just buy a monitor
A real second monitor is still better, and I'm not going to pretend otherwise. More pixels, better color, no battery to manage. But a second monitor also costs money, takes up desk space, and needs a cable and a wall outlet. A second screen made from a phone you already own costs nothing and folds away when you're done.
Where it actually earns its spot on your desk:
- Keeping Slack, email, or a chat window visible without alt-tabbing out of what you're writing
- Parking a reference doc, a spec, or a video call on the side while you work in the main window
- Extra space on a laptop that only has one screen and you're cramped between two apps
- Working from a coffee shop or a hotel room where hauling a monitor isn't realistic
Where it doesn't help: anything that needs real color accuracy, or anything where you'll be staring at that screen for hours. A 6-inch panel is a sidebar, not a workstation.
The apps that actually work
I tried four different ones over about two weeks. Two were worth keeping installed.
spacedesk (Windows, free) was the surprise winner. It turns almost any phone or tablet into a wireless second display for a Windows laptop, and the free tier does everything most people need. Setup is a driver install on the laptop and an app on the phone — both need to be on the same Wi-Fi network, and that's it.
Luna Display or Sidecar (Mac) if you're in Apple's ecosystem. Sidecar is built into macOS already and works with an iPad for free — no extra app needed, just a toggle in Control Center. Luna Display costs money but adds support for using an iPhone or an Android tablet the same way, with generally lower lag than Sidecar over Wi-Fi.
Duet Display works across both platforms and supports USB connection, which matters more than people expect — more on that below.
I didn't get anywhere with a couple of the free Android-only options; connection kept dropping, or the resolution was locked to something unusable. Your mileage may vary depending on the phone.
The one setting that decides whether this feels smooth or annoying
Here's the part nobody mentions in the "how to" posts: wireless second-screen apps route your video over Wi-Fi, and if your router or your phone is having a mediocre day, you'll feel it as cursor lag and dropped frames. It's usable for a static reference window. It's not usable for dragging a video timeline around.
The fix is connecting over USB instead of Wi-Fi when the app supports it. spacedesk, Duet Display, and Luna Display all let you plug the phone in directly, and the difference is not subtle — it goes from "this feels like a laggy remote desktop session" to "this basically feels wired in." The catch is that this only works if your cable actually carries data, not just power. I've written before about how a lot of USB-C cables floating around a house are charge-only, and this is exactly the kind of moment that trips people up — you plug in, the app just sits there waiting for a device, and the actual problem is the cable, not the software.
Say you're setting this up with a phone that's been sitting in a drawer for a year: grab the cable it originally shipped with if you still have it, since that one's guaranteed to carry data. A random cable from the junk bin is a coin flip.
Setting it up without wasting twenty minutes
Photo by Andrea Piacquadio on Pexels
A realistic walkthrough, using spacedesk on Windows as the example since it's free and the most forgiving:
1. Install the spacedesk driver on your laptop and the spacedesk app on your phone from its app store. 2. Connect both to the same Wi-Fi network, or plug the phone into the laptop with a known-good data cable. 3. Open the phone app — it should show your laptop's name under available connections. Tap it. 4. On the laptop, right-click the desktop, go into display settings, and you'll see the phone listed as a new monitor. Set it to "extend" rather than "duplicate." 5. Drag the display arrangement in settings so it matches where the phone physically sits relative to your laptop screen — otherwise your mouse will jump the wrong direction when you move between them.
That last step is the one people skip and then decide the whole thing is broken. It's not broken, the arrangement is just backwards.
What I actually use mine for
Honestly, it's become the place my calendar and a running task list live, propped up on a cheap stand to the right of my laptop. Nothing dramatic. But not having to alt-tab out of whatever I'm writing just to check what's next on my day removes a small amount of friction, dozens of times a day, and that adds up more than any single big feature would.
I was skeptical this would stick — I've tried a lot of tools over the years that were fun for a weekend and then quietly stopped getting used. This one's still on my desk a month later, which for me is the real test.
FAQ
Does this drain my phone's battery fast?
Yes, noticeably, if you're running it wirelessly for hours — the screen and the constant network activity both pull power. Keeping the phone plugged in while it's acting as a monitor solves this and also gives you the better USB connection, so it's worth doing both at once.
Can I use a tablet instead of a phone?
Better, if you have a spare one. More screen space for the same setup, and the apps above all support tablets the same way. An old iPad that's too slow for daily use is often perfectly fine as a second screen, since it's just displaying, not doing heavy processing.
Will this work with a Chromebook?
Support is spottier there. spacedesk has had inconsistent results on Chrome OS depending on the model, and Sidecar and Luna Display are Mac-only on the laptop side. If a Chromebook is your main machine, test the free tier of an app before assuming it'll work the way it does on Windows or Mac.
The takeaway
You probably don't need a new gadget to get a second screen — you likely already own one, sitting in a drawer. The setup takes about ten minutes, the software is free or close to it, and the only real trap is using a charge-only cable and blaming the app when nothing happens. If you've got an old phone doing nothing, it's worth the ten minutes to find out if this is one of those tools that actually earns a permanent spot on your desk, instead of another thing you tried once and forgot about.
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