Samsung Auto Blocker Blocks USB Debugging: How to Fix ADB

Samsung Galaxy phones with One UI 6 and newer include a security feature called Auto Blocker. Among other things it blocks commands sent to the phone over a USB cable. When it is on, USB debugging may refuse to turn on, the phone may not appear in adb devices, or installs from a computer fail. This guide shows how to check it and how to switch it off while you work.

What Auto Blocker does

Auto Blocker protects the phone against attacks through apps from unknown sources and through the USB cable. Its options differ a little between One UI versions, but they include:

• Blocking apps from unauthorized sources
• Checking apps for malware
• Blocking commands by USB cable
• Blocking images in messaging apps that may contain hidden code

The USB protection is what gets in the way of ADB. On some versions you cannot even switch USB debugging on while Auto Blocker is active.

Symptoms

• USB debugging is greyed out or switches itself off again.
• A message says the action is blocked by Auto Blocker.
• adb devices shows nothing, although the cable and driver are fine.
• APK installs from the computer are refused.

How to turn Auto Blocker off

1. Open Settings › Security and privacy.
2. Tap Auto Blocker (on some versions it sits under More security settings).
3. Turn it off, or keep it on and turn off only Block commands by USB cable if your version offers that option.
4. Go back to Settings › Developer options and switch USB debugging on.
5. Reconnect the cable and accept Allow USB debugging? on the phone.

If you use Maximum restrictions (a stricter mode on recent One UI versions), turn that off too, because it keeps Auto Blocker on.

Turn it back on afterwards

Auto Blocker is a useful protection, especially on a phone you carry every day and plug into public chargers. When you finish debugging, switch USB debugging off and Auto Blocker back on.

Other Samsung checks

• Samsung USB driver on Windows. Without it the phone is not detected. See adb devices shows no devices.
• USB mode. Pull down the notification shade and choose Transferring files in the USB options.
• Knox or work profiles. Company-managed phones may block USB debugging by policy. Ask your IT team.

With ADBKit

ADBKit connects to the phone through Chrome or Edge with WebUSB, so it is affected by Auto Blocker in the same way. Turn it off as above, then connect again. Over Wi-Fi with Wireless debugging the USB cable protection does not apply, but you still need Developer options and Wireless debugging switched on.

For the Samsung-only flashing mode, see Samsung Download mode.