Heads up or “peeking” notifications, the little miniature pop-ups that appear in Android Lollipop if a notification comes in when you happen to be actually using your device, aren’t for everyone. That’s why Google will include the option to disable them on a per-app basis in the upcoming Android M release. (See Settings>Sound & Notification>App notifications in the Developer Preview.) It’s also why apps like HeadsOff have sprung up to cater to those who want them to go away even sooner.
No, Google Won’t Enable Ticker Text If You Disable Heads Up Notifications (Peeking) In The Android M Developer Preview was written by the awesome team at Android Police.