Google has done something in Android 4.2 that is good for some of their older users. They have hidden the Developer settings. For most of their older users, they don't need these, and might turn them on by mistake and play with them if they are in plain sight. So Google has hidden them to keep that from happening.
When you go into settings, you'll notice no Developer settings. So here's how you get around that:
- Tap Settings
- Tap About Phone
- Tap the Build number 7 times, yes 7 times.
- Voila! You've got developer settings again.
So that's that. But if we didn't tell you, you may never have found it. You'll also need this to unlock the bootloader and to root your device. We'll be putting up some more Android 4.2 and Nexus stuff over the next few weeks so stay tuned.
Source: Android Central