One of the new features of Android Lollipop is the Heads-up notifications, which are small floating windows that appear when you receive call, message or app alert. In theory they are useful because they let you respond or dismiss a notification without leaving the app you are in, but in real life they are too invasive and annoying, especially when you receive many messages, for example from WhatsApp.
Unfortunately, Google has not provided any proper option to disable the Heads up notifications on Lollipop, though Android 5.1 has a small fix for this by enabling you to swipe upwards to hide them. Also, if you do not have the 5.1 update yet, you can control how many you get with Priority mode settings, but that does not fully disable the heads up notifications.
Here is how to disable heads up notifications completely on Android Lollipop without root access. All you need a little app ‘HeadsOff’ installed on your phone. This free app will disable all Lollipop Heads-up notifications on your phone, though it will not bring back the KitKat approach to notifications.
The working of the app is very simple. Once installed it from the Play Store, only need to enable the service from within the program.
HeadsOff has also a pro version, which lets you disable Heads-up notifications for individual apps. Also, it restore the ticker text in the status bar to see a little notification preview.