Galaxy Gear 2 Start: sdb devices "No device listed"

When I first started prepare my development environment for Samsung Galaxy 2, a pretty trivial problem stops me. After I installed Tizen SDK and plugged my device to my laptop, I can not see it from "sdb devices". The result is just empty device list as below:

shuang@shuang-box:~$ sdb devices
List of devices attached

I keep searching the solution for this problem without result. There is a post on Tizen developer forum discussing the same problem: https://developer.tizen.org/forums/general-support/sdb-does-not-list-connected-test-device. But all the advice there have no effects for my case.

Then I realized it could be the setup on Galaxy Gear 2, so I press the system setup button and in the gear info sub-menu I found USB debugging  check box. There it is! I checked it and it works now.

shuang@shuang-box:~$ sdb devices
List of devices attached 
538131fd41001cb6 device SM-R380