How to Fix the ADB Device Unauthorized Error on Android

If adb devices lists your Android phone as unauthorized, the computer can see the device but has not been approved to use ADB with it. The fastest fix is to unlock the phone, reconnect it, and accept the Allow USB debugging? RSA prompt. If that prompt never appears, revoke existing USB debugging authorizations, restart ADB on the computer, and reconnect.

This is an ADB authorization problem, not a sign that your phone must be rooted or that its bootloader must be unlocked. Google documents the RSA confirmation prompt as a security protection on Android 4.2.2 and later. See the official Android Debug Bridge documentation.

What “ADB device unauthorized” means

Run this command from a terminal or Command Prompt where ADB is available:

adb devices

A working USB connection should show a device serial followed by device. If the same serial is followed by unauthorized, Android has not accepted the ADB host key for that computer yet.

Fix the ADB unauthorized error

1. Unlock the phone and look for the USB debugging prompt

Keep the phone unlocked while it is connected. If Android shows Allow USB debugging?, verify that you recognize the computer and tap Allow. On a computer you personally control, you can also select Always allow from this computer so Android remembers that host key.

If there is no prompt, continue with the reset steps below.

2. Revoke old USB debugging authorizations

Open Settings > Developer options. On many current Android devices, Developer options is under Settings > System, although manufacturers can place or name it differently. Google notes that Android 4.2 and later hides Developer options until you enable it.

1. Turn USB debugging off.
2. Tap Revoke USB debugging authorizations (the wording may vary slightly by device).
3. Confirm the reset.
4. Turn USB debugging on again.

The official Developer options guide explains where USB debugging is located on different Android versions.

3. Restart the ADB server on the computer

Disconnect the phone, then run these commands one at a time:

adb kill-server
adb start-server

Google recommends restarting the ADB server when the connection becomes unresponsive. You can also run adb devices after adb kill-server; any subsequent ADB command can start the server again.

4. Reconnect with a data-capable USB cable

Reconnect the phone directly to the computer, preferably without a hub. Keep the screen unlocked and watch for the RSA authorization dialog. Tap Allow when it appears.

You do not normally need to switch between “File transfer” and “Photo transfer” just to authorize ADB. USB debugging is the important setting. However, if the computer does not detect the phone at all, try another known-good data cable or USB port. Google’s hardware-device troubleshooting guide also recommends testing another cable when a device is not detected.

5. Verify the device is authorized

Run:

adb devices -l

The status should now be device, for example:

List of devices attached
R9CT304B7K    device

If the phone still shows unauthorized

Work through these checks before changing anything more invasive:

• Update SDK Platform-Tools. Google recommends using the latest Platform-Tools because current ADB releases remain backward compatible with older Android versions. Get them through Android Studio’s SDK Manager or the official SDK Platform-Tools page.
• Restart the phone and computer. Then repeat the revoke-and-authorize sequence with the phone unlocked.
• Check Windows USB drivers. If Windows does not properly expose the phone to ADB, install the manufacturer’s driver. Google maintains an official OEM USB driver directory. Google devices on Windows use the Google USB Driver.
• Distinguish authorization from detection. If adb devices shows no serial number at all, troubleshoot the cable, USB port, driver, or Linux device permissions first. That is different from an unauthorized status.

Why revoking authorization works

ADB uses a host key to identify the computer. Android asks you to approve that key before allowing debugging commands. Revoking USB debugging authorizations clears previously trusted computers on the device, so the next connection can establish a fresh authorization. That is why the reset is more reliable than changing the phone’s ordinary USB file-transfer mode.