Search engine giant Google has announced has officially announced the latest update Android Lollipop 5.1. But as of now, this update is available only for the selected Nexus device, which includes, 2012 Wi-Fi Nexus 7 (Nakasi), the GSM/LTE Nexus 5 (Hammerhead), and the Nexus 10 (Mantaray).
This updates mainbly contains bug-fixes, along with it, bringing some new improvements such as OS-level support for dual SIM card slots as well as HD voice. Moreover, it also has the ability to join Wi-Fi networks or connect with paired Bluetooth devices and a new device protection feature.
As per Google, device protection feature will help you with your lost or stolen device, which will remain locked until you sign in with your Google account, even after resetting the device.
As usual, Google posted the Android 5.1 factory images and binaries for Nexus devices on its very own developer website and the source code in Android Open Source Project (AOSP). Moreover, the factory images and binaries were only released for the selected Nexus device, which includes Nexus 5, Nexus 10 and Nexus 7 (2012) Wi-Fi devices.
You can access the it in android.googlesource.com and the source is provided under tags "android-5.1.0_r1" and branches "lollipop-mr1-release".