Google Inc. released the Android 5.1 update Monday, a new version of its Android Lollipop operating system that fixes a number of problems with earlier releases and includes a few new tricks. Google is rolling out the update now for the Nexus 4 and Nexus 5 smartphones, as well as the Nexus 7 tablet.

Google’s new Nexus 6 from Motorola is not mentioned in the the press release announcing the Android 5.1 update, and the smartphone also did not show up in documents released before the official announcement by T-Mobile that were spotted by Android Police. The carrier’s support documentation for the Nexus 4, Nexus 5 and Nexus 7 all mention Android 5.1, but no mention of the new Lollipop update is found on the support page for the Nexus 6 as of this writing.

Android 5.1 features support for phones with dual SIM, and also includes the ability to change colors for the phone dialer app depending on which SIM card a user has selected. With the update, Lollipop also includes HD voice calling for select devices, as well as new quick settings for Wi-Fi and Bluetooth.

Lollipop’s oft-maligned volume alert modes now include an alarm function that allows wake-ups even when the phone is set to the “none” or “priority” alert modes, and also allows users to swipe up to clear notifications without disabling them permanently. Google claims Android 5.1 also includes “stability and performance” improvements, as well as new security features for the Nexus 6 -- when it arrives on the Motorola-made smartphone.

“With Device Protection, your lost or stolen device will remain locked until you sign in with your Google account -- even if someone resets your device to factory settings. This feature will be available on most Android phones and tablets shipped with Android 5.1 in addition to Nexus 6 and Nexus 9,” David Burke, Google’s vice president of Android, said in a statement.