This post is original on droidchina. thanks for the guys there, and all credit to them.
In Android 4.2, developer options menu is not visible by default. Follow the steps below to enable it.
- Go to Settings > About phone (or tablet)
- Find the build number
- Start tapping on Build number repeatedly. You will see a message saying “You are now X steps away from being a developer”
- Continue tapping till you see “You are now a developer!” message.
- Go back into Settings and you should see Developer options menu.