"Could not connect to device": fixing the Android File Transfer error

You plug the phone in, Android File Transfer opens, and instead of your folders you get "Could not connect to device. Try connecting or restarting your device." Other apps word it differently. OpenMTP shows an empty window or no device, and Android File Transfer has a second version of its own: "Can't access device storage. If your device's screen is locked, disconnect its USB cable, unlock your screen, and then reconnect the USB cable."

All of them mean the same thing: the app asked the phone for a file session and did not get one. Work through these in order: unlock the phone and choose File transfer in its USB notification, quit every other app that might be holding the phone, then try another cable and port. That fixes it nearly every time. If the phone does not appear on the Mac at all, in any app, start with Android phone not showing up on Mac instead. This page is about the error.

What the error means

Android File Transfer, OpenMTP and similar apps talk to the phone over MTP, the Media Transfer Protocol. macOS has no MTP support of its own, so each app opens the phone's MTP interface over USB by itself, and Android's MTP server accepts one session at a time. So the error turns up in four situations:

• The phone is not offering MTP at all, because its USB mode is set to charging only.
• The phone offers it but keeps its storage closed, because the screen is locked.
• Another app on the Mac got to the phone first and is holding the session.
• The link itself is bad: a cable that only charges, a worn port, or a hub that drops the connection.

If you want the longer story of how MTP works and why it behaves like this, see MTP explained.

The fixes, in order

1. Unlock the phone and choose File transfer

Most phones only charge when you plug them in, and MTP is off until you say otherwise. Unlock the phone, pull down the notification shade and tap the USB notification.

• Pixel: tap Charging this device via USB, then under Use USB for choose File transfer (shown as File transfer / Android Auto on recent versions).
• Samsung Galaxy: tap USB for charging phone, tap it again for more options, and choose Transferring files / Android Auto.
• Other makers: the words differ, but you want the option that mentions files or MTP, not PTP or photos.

Samsung changed its default in One UI 8.0 to Charging phone only, so a Galaxy that worked with your Mac before an update can start showing this error after it. Choosing the mode again fixes it.

If you are tired of choosing every time, Android has a setting for the default. Turn on Developer options (see how to turn on USB debugging, which starts with the same step), then open Developer options > Default USB configuration and choose File transfer. On a Pixel, Developer options is under Settings > System.

2. Quit every other app that might hold the phone

Only one app can hold the phone's MTP session, and several Mac apps reach for any phone or camera that appears. OpenMTP's own troubleshooting list names Preview, Google Drive, Dropbox, OneDrive, Android File Transfer, Garmin Express, iMovie and Lightroom. Add Photos and Image Capture if either opened when you plugged the phone in. Quit them all, unplug the phone, and plug it in again.

Android File Transfer also installs a helper, Android File Transfer Agent, that starts at login and opens the app whenever a phone appears. If you use a different MTP app, that helper is in the way. Remove it from System Settings > General > Login Items & Extensions, or uninstall Android File Transfer.

3. Remove Samsung Smart Switch

Smart Switch for Mac is known to block other apps from reaching a phone over MTP. Samsung's own troubleshooting for Mac connections starts by uninstalling it: open the Smart Switch installer disk image and click Uninstall app. OpenMTP says the same: if its window goes blank with a Samsung phone, uninstall Smart Switch. You can install it again later if you need it for moving to a new phone. The same goes for Kies, Samsung's older desktop app, if it is still on an old Mac.

4. Reset the connection

With the phone plugged in, switch the USB mode to PTP and then back to File transfer. Users on the Android forums reported that this cleared the error when replugging did not. If it still fails, restart the phone, then restart the Mac. In the same thread, restarting the Mac was what finally fixed it for one user.

5. Try another cable and port

Plug the cable straight into the Mac, not into a hub, a dock or a monitor, and try a different port. Then try a different cable, ideally the one that came with the phone or one you know carries data. Some USB-C cables only charge, and they look exactly like the ones that do not.

Your Mac can tell you whether the cable is carrying data. Hold the Option key, open the Apple menu and choose System Information, then select USB. If the phone is listed, the cable carries data and the problem is further up this list. If it never appears in any USB mode, suspect the cable or the port. How to check a USB-C cable on a Mac goes through it step by step.

The route that avoids MTP

If the error keeps coming back, there is a second door into the phone. Android's developer connection, adb (Android Debug Bridge), uses USB debugging rather than MTP. It does not care which USB mode the phone is in, and apps that grab MTP devices do not touch it. What can hold it is another adb program, such as Android Studio, scrcpy or an adb server you left running, and those are easy to find and quit. adb and MTP compared covers the differences in detail.

You can use that route in three ways:

• Google's platform-tools in Terminal. Free. adb pull and adb push copy files, with no window and no Finder.
• An app with an ADB mode. MacDroid, for example, offers ADB as well as MTP.
• SideMount. It speaks adb itself, straight over the cable, and mounts the phone as a volume in Finder. Every Mac app can then open and save files on the phone in place, and there is no adb server or anything to install on the phone.

Each needs USB debugging turned on once, and the Mac allowed on the phone. SideMount also needs its file system extension turned on once in System Settings, and macOS 26 or later. The setup guide walks through both.

Questions