Using the LED notification light to be informed about missed calls, new messages, voice mail is a common way in smartphones and on the new HTC One M8, you can easily specify which notifications to be informed via the LED notification light.
To manage customize LED notification light on HTC One M8, do as follows:
1. Open Settings and under Phone settings, go to Display & Gestures menu
2. Under Display settings, open Notification light.
3. Now mark/unmark the events you'd like to be notified about via the Flash LED Light. Available options are: missed call. voice mail, messages, calendar, mail, and alarms