Turn existing iPhones and iPads into Mac second monitors without subscriptions or dedicated hardware
Pull out an iPhone or iPad sitting on your desk and connect it via cable to extend your Mac's display to that device. Without separate subscription fees or additional hardware, you can use devices you already own like true external monitors. This repository is a free open-source tool that removes the limitations of Apple's Sidecar and implements that functionality.
Filling the gap in existing solutions
Apple's Sidecar is free but requires the same Apple ID and does not support iPhones. Duet Display has switched to a subscription model, and Luna Display requires dedicated hardware. This project solves the problem without an account, without spending money, and with just a cable. In particular, the ability to use an iPhone as a display is a significant difference compared to other paid solutions. Furthermore, it is a true extended mode where you can drag windows to move them, rather than simply mirroring the screen.
Connection methods and input support
Connecting via USB cable transmits the screen with the lowest latency, while using Wi-Fi allows the device to be discovered without separate configuration. The screen is displayed sharply at Retina resolution, and rotating the device vertically reconfigures it as a vertical monitor. The iPhone's touchscreen can be used as a mouse and trackpad for the Mac, allowing you to click by tapping, drag, and scroll with two fingers. This feature is implemented through Mac accessibility permissions, and Apple Pencil support currently remains on the roadmap.
Performance and quality adjustment
Screen transmission uses hardware encoding to minimize latency. The default settings already select the sharpest image quality, but when watching videos with a lot of motion or playing games, you can lower the quality settings to increase the frame rate. When using a 5K iMac as the receiver, 1:1 transmission at 5120x2880 resolution is possible through HEVC encoding. According to measurements, latency when connected via cable is between approximately 12ms and 33ms, which means you can balance quality and smoothness depending on your use case.
Pre-use considerations
Because this tool uses private Mac APIs, it cannot be distributed via the App Store and carries the risk of stopping working during macOS updates. Additionally, it requires screen capture and input injection permissions, so users who prioritize privacy should be aware of this. Data is transmitted directly between devices without going through a server, so security is high, but it may be unencrypted during Wi-Fi transmission. The developer is currently on vacation until November 17, so bug fixes or new feature additions may be delayed.
