You'll see the following improvements when upgrading from 5.0 to 5.1:

• Phone protection. If your phone gets lost or stolen, it will remain locked until you sign in with your Google account, even if someone resets it to factory settings. To automatically enable this feature, set up a Google account on your phone and set a screen lock (PIN, password or pattern). It's your kill switch, making your phone useless when stolen but allowing you to get it back in working order when recovered.
• Expanded quick settings. In quick settings, you can now quickly switch between Wi-Fi access points or paired Bluetooth devices with the menu on each tile. Also, some quick settings, like Hotspot, don't appear until you use the feature for the first time; if you don't use the feature often and want to remove it from quick settings, touch & hold the setting's icon.
• Improved notifications. If you're using an app and a high-priority notification arrives (such as an incoming call or an alarm), a small notification pops up briefly over your current app so that you can take action. You can now swipe sideways to dismiss it.
• Improved downtime and interruptions. You can enter a scheduled downtime early. You can also block interruptions until your next alarm, instead of missing an alarm when you choose Don't interrupt.

If you are not familiar with features in Android 5.0, see the sections below.

You will quickly notice a whole new material design - an updated colorful look and feel on your phone that includes more fluid, meaningful motions, new application and system themes, colors and widgets.

• Lock screen notifications. View and respond to notifications directly from your lock screen, while still hiding sensitive content behind it.
• Notification rules. For fewer disruptions, press the Volume button to turn on Priority mode so that only certain people and notifications get through. Or, schedule recurring downtime when only Priority notifications get through.
• Dismissing notifications. You can still touch a notification to open it, or swipe left or right to dismiss it. To dismiss all notifications, touch below the notification list. (In Kit Kat, is at the top of the list.)
• High-priority notifications. When a high-priority notification (such as an incoming call or an alarm) arrives while you are using the phone, the notification pops up briefly over the current application so that you can take action and then retreats to the notification shade.
• Cloud-synced notifications. When you dismiss a notification on one device, it will be dismissed on your other Android devices if they are connected to the internet.

Get to the most frequently used settings by swiping down twice from the top of the screen.

• New controls include active hotspot, screen rotation, and screen casting.
• Easier on/off toggles for Wi-Fi, Bluetooth, and location. Touch Wi‑Fi and Bluetooth labels to quickly access settings.
• Manually adjust screen brightness for certain conditions.

You can manage which notifications you see when your device is locked: all, none, or only priority interruptions. You can set certain apps to have priority notifications, sensitive notifications or blocked notifications.

Also, you can define your downtime, regular intervals when you don't want interruptions. Your phone will screen incoming calls and messages, allowing only certain types of notifications from specific contacts during that time. For example, you can allow only priority interruptions during weekends.

The navigation buttons at the bottom of the home screen have a different look and some expanded funtionality.

Button	Lollipop	Kit Kat
Home
Back
Overview (was Recents)

The button still opens a list of apps that you've recently used, but now includes activities within those apps for a consistent way to switch between tasks. For example, tabs that are open in Chrome, your Gmail Inbox and a draft email message are listed as separate cards. You can exclude Chrome tabs if you don't want them in your recent list.

You can pin your screen to keep a specific app or screen in view. For example, you can “pin” a game to prevent a child from navigating to anywhere else on your phone.

Battery Saver extends phone use by up to 90 minutes by automatically turning on when the battery is low to reduce performance and limit background data operations.

The estimated time left to fully charge is displayed while your phone is charging.

The estimated time left before you need to charge your phone is displayed.

With Android Lollipop, your phone will not connect to a Wi-Fi access point unless there is a verified internet connection. This feature improves hand-offs between Wi-Fi and cellular connections, helping to maintain your video chat or voice-over-IP (VoIP) call as you switch.

ART, an entirely new Android runtime, improves application performance and responsiveness. After upgrading to Android Lollipop, your applications will undergo a one-time optimization process. Note that the optimization for ART requires more storage space.

Android Lollipop includes Smart Lock, which bypasses your screen lock and keeps your phone unlocked in situations you specify:

• When paired with a trusted device, such as your Moto 360, a Bluetooth car kit or headset. Smart Lock replaces previous trusted device capability in your Motorola phone. You will need to add your trusted devices again: Settings > Security > Smart Lock.
• When you're at a trusted place, like work or home.
• When it recognizes your voice.
• When you're carrying it in your hand or bag.

Encryption can now use a stronger 256-bit key to help protect your data. The stronger key will only be used after you perform a factory reset on Android Lollipop. Otherwise encryption will continue to use 128-bit key.

• Search the Settings app to find what you need quickly.
• People app is now called Contacts.
• Adaptive brightness replaces auto brightness.