Google announced that starts the spread of Android 5.1, which offers better security, HD calls and support for working with multiple SIM cards.
Android 5.1 includes improvements in stability and performance, and it brings compatibility with HD calls forcertain devices and support for working with multiple SIM cards.
Users can now connect to Wi-Fi networks and control the paired Bluetooth devices directly from the quick settings menu.
The biggest change, however, is linked to the security of the devices. With Android 5.1 users can tweak the device wants mandatory login with Google account, even after resetting to factory default settings. This option is available for most phones sold with Android 5.1 and for Nexus and Nexus 6, 9.
So even if you lose your phone or it is stolen, the device will be useless if not entered your password.