If you encounter "ADB device not found" or "unauthorized" errors, try these steps: 1. Check USB cable and enable Developer Options & USB Debugging. 2. Authorize the computer via the RSA prompt on your device. 3. Restart ADB with adb kill-server then adb start-server. 4. Change USB mode to File Transfer. 5. Update USB drivers. 6. Test with another port or computer.

If you are encountering "ADB device not found" or "unauthorized" errors during Android development, it's typically related to ADB (Android Debug Bridge) connectivity or device authorization. Here are the steps to resolve these issues:

The operating environment of this tutorial: Samsung Galaxy S24, Windows 11

1. Check USB Connection and Developer Options

Ensure that your device is properly connected and configured for debugging. A faulty cable or disabled settings can prevent ADB from detecting the device.

• Use a high-quality USB cable known to support data transfer
• On your Android device, go to Settings > About Phone and tap on "Build Number" seven times to enable Developer Options
• Navigate to Settings > Developer Options and turn on "USB Debugging"
• Also enable "OEM Unlocking" if available

2. Verify Device Authorization Prompt

When USB Debugging is enabled and the device is connected, Android should display an authorization dialog asking to allow USB debugging for your computer's RSA key. If this is blocked or dismissed, the device appears as unauthorized.

• Disconnect and reconnect the USB cable
• Look for a popup on the phone titled "Allow USB debugging?" with the computer's RSA fingerprint
• Tap ALLOW to authorize the connection
• If the prompt does not appear, revoke existing authorizations in Developer Options under "Revoke USB debugging authorizations", then reconnect

3. Restart ADB Server

Sometimes the ADB server process becomes unresponsive or fails to recognize newly connected devices. Restarting the server forces it to rescan attached devices.

• Open a command prompt or terminal on your computer
• Run adb kill-server to stop the ADB server
• Then run adb start-server to restart it
• Alternatively, use adb devices which will automatically start the server and list connected devices
• If your device shows up as "unauthorized", disconnect and reconnect it after restarting ADB

4. Change USB Connection Mode

The default USB mode may not support ADB. You need to explicitly select a mode that enables file transfer or developer features.

• Swipe down the notification panel while the device is connected via USB
• Tap on the USB connection notification
• Select File Transfer or MTP Mode instead of "Charging only"
• Some devices label this option as "Transfer files" or "PTP"
• This change often triggers the ADB handshake and authorization prompt

5. Update or Reinstall USB Drivers

Outdated or missing USB drivers prevent proper communication between your PC and Android device, especially on Windows systems.

• Download the latest USB driver from your device manufacturer’s official website (e.g., Samsung, Google, OnePlus)
• Install the driver and reconnect the device
• Alternatively, use Google USB Driver through Android SDK Manager if developing for Pixel devices
• In Device Manager, locate your device under "Other devices" or "Portable Devices", right-click, and choose "Update driver"

6. Try a Different Port or Computer

Hardware issues such as a damaged USB port, low-power hub, or interference can disrupt ADB detection.

• Connect directly to a USB port on the computer, avoiding hubs or extension cables
• Try a different USB port, preferably USB 3.0 or higher
• Test the device on another computer to isolate whether the issue is with the machine or the device
• If the device is recognized elsewhere, focus troubleshooting on the original computer’s ADB setup or drivers

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