When something is not right.

The app says no phone is connected

Check the cable first: charge-only cables have no data lines. Try a port on the PC itself rather than a hub.

Unlock the phone. If it asks to allow USB debugging, tick Always allow from this computer and tap Allow.

If Windows sees the phone but the app does not, the app offers Repair USB driver in the bar above the mirror. See Fix a phone Windows will not read.

Windows says "USB device not recognised"

Windows gave up reading the phone. The app notices within a few seconds and offers Fix USB, which resets the device after one administrator approval, and Fix automatically from now on.

If it keeps happening, try another cable, turn off USB selective suspend in Windows' power options, and choose File transfer in the phone's USB options. rex usb status shows what Windows reports.

The lock screen is black

Some phones mark their secure lock screen as protected, and Android will not stream it. After a restart you may need to unlock on the phone once.

For a pattern lock, the app draws a guide so you can unlock from the PC: see Unlock a phone whose lock screen is black. The pattern is never stored or replayed.

There is no sound from the phone

Click the sound button in the top bar: when there is nothing to control, its panel says why. Phone audio needs Android 11 or later. Check that Phone audio on this PC is on, then restart the mirror: audio settings apply the next time it starts.

If the panel shows a level but nothing plays, check it is not muted there or by a rule in Sound on this PC, and look for Android Headless Mirror's scrcpy in the Windows volume mixer.

Only the main view plays sound; copies are always silent. Some apps refuse to let their sound be captured.

The picture stutters or lags

Lower the resolution or the frame rate, and use USB rather than Wi-Fi. Each copy of the phone asks the phone for another video encoder, so close copies you do not need.

If the picture flickers or stays black, try another renderer.

Keys type the wrong characters

The phone uses its own hardware keyboard layout. Keyboard layout in Controls opens the Android screen where you pick it.

If typing still misbehaves, turn on the compatibility keyboard and restart the mirror.

A shortcut from anywhere does nothing

Check that Shortcuts work while the window is hidden or behind others is on; the tray menu has the same switch. The app must be running, in the tray at least.

Windows gives no app the keys while a program running as administrator is in front, so they do nothing then. Another keyboard tool, such as AutoHotkey or PowerToys, may take the key first: choose a different one. The settings say when another app has claimed a key, or when your keyboard layout types a character with it.

A copy will not open

Copies need the phone upright and enough room beside it at full height. Make the window wider or close the side panel with Ctrl+Alt+B.

A copy that fails twice is given up on: the phone may have no video encoder left for it.

An app is missing from the Apps tab

An app installed since the list was read appears after Read again at the top of the tab, or the next time the phone connects. Apps that came with the phone are in their own group only with Show system apps on, though a search always finds them. An app you hid is back with Show hidden apps at the end of the tab.

Only apps with a launcher icon are listed, and apps in a work profile are not.

A file will not send or an APK will not install

The item in Controls gives the phone's reason. Free some storage for “no space left”, reconnect the phone for “disconnected”, or use Try again after fixing it. Cancelling removes the partial copy.

An older APK needs Allow installing an older version; a test-only APK needs Allow test builds. Files may only go inside shared storage, such as /sdcard/Download/.

The second screen does not open

It needs Android 10 or later; Controls says so on an older phone. Some apps refuse to run on another display, and Android then says it could not open them there. If the phone is locked, unlock it: some phones show a second display only while unlocked.

It tries once more when it fails, then says why. With very little room in the window it shows instead of the phone until there is room beside it.

A profile did not change everything I expected

A profile changes only the settings in it; Show what it changes in its menu, or rex profile show <name>, lists them. Settings that decide how the mirror starts need a restart: the app offers one, or does it at once if set to.

A profile that switched on by itself puts back only the settings you have not changed since. One saved by another version applies what this version still knows and says how many of its settings it no longer uses. The battery rule is off on a PC with no battery.

The second phone does not show

It must be allowed for USB debugging, like the first; until it is, the phone menu lists it as waiting. One phone on USB and Wi-Fi at once is the same phone and is never shown beside itself. If you once chose Never for this phone, it is not asked about again, but the phone menu can still show it beside.

With three or more phones, two show at a time: choose them from the phone menu. A window too narrow for both shows the main phone alone until there is room. Copies wait while two phones show.

A key of my own is refused, or does nothing

The words under its box say why it was refused: another action has it, Windows keeps it for itself, a shortcut from anywhere takes it first, or it would fire while you type into the phone (a key for the window needs Ctrl, Alt or Win, or is F1 to F24 on its own). Keys for the window work while the window is in front; for a key that works anywhere, use Shortcuts from anywhere.

Put every key back under Keyboard shortcuts returns them all as the app ships, and rex keys reset does the same from a terminal.

The mirror stopped by itself

If Stop the mirror after is set, the status line says it stopped after that time, and it stays stopped until you press Start. If it says the phone has no video encoder by some name, choose another under Video encoder, or let the phone choose. If it keeps closing, it is started again as many times in a row as Times in a row before it stops trying says, then waits for you.

The app does not start, or closes

The log says exactly why. Open it from the folder below, or run rex diagnostics: it reports the version, the program Windows starts at sign-in and whether it is this one, whether the settings files can be read, and whether scrcpy and ADB run.

Then report the problem with that report attached.

Where the app keeps its files

Installed, the app's own files are in %LocalAppData%\Programs\Android Headless Mirror, and your settings, logs, screenshots and recordings are in %LocalAppData%\REX\Android Headless Mirror.

config.json holds the app's settings, state.json what it remembers about your phones and the window, and logs\mirror.log what happened.

Put every setting back

Settings → Connection & advanced → Reset every app setting. From a terminal, rex config restore undoes the last change made with rex config set.

Uninstall

Windows Settings → Apps → Android Headless Mirror → Uninstall. Your settings stay in %LocalAppData%\REX until you delete that folder.

Privacy and security

There is no account and no telemetry. The app does not upload the mirrored screen, what you type, lock information or anything on the phone. It connects to GitHub only to download itself and the official scrcpy, and, if you turn on Check for a newer version once a day in Settings, Startup & tray, to ask which version is newest. That check is off unless you turn it on.

USB debugging gives this PC full control of the phone, so only allow computers you trust. The app never stores or types a PIN, password or pattern, and asks for administrator approval only for the USB repairs, through the Windows prompt.

Report a problem

Open a new issue on GitHub, or use Report a problem in the Info tab, which fills in the version. Attach the output of Copy diagnostics (Info tab) or rex diagnostics.