Alarm clocks aren't working on Android 6 I recently moved to Android 6 and promptly slept in the next day as my alarm clock (Alarm Xtreme) wasn't waking me up.

I search around a bit, disabled the energy setting stuff for that application and went to bed...only to not being waken up again.

I read some more and some people suggested a different alarm app ("Simple Alarm Clock" that apparently should work on Marshmallow). I set up my alarms and then went on to close the application as I always do (rectangle button, push the application window 'out') only to see the little alarm bell icon in the status bar disappear. 

I went back to the Alarm Xtreme application, opened it and sure enough the alarm bell symbol appeared. Closed the app and the symbol immediately disappeared.

What is going on there and how do I fix it? Aren't alarms running in the background anymore? If yes why not?

I don't want to always remind me to open the alarm app before going to bed, mostly because I'd forget it half the time.

Oh also because that is mentioned a lot: My phone is always plugged in when I sleep.
When you say the little alarm status bar symbol, do you mean up the top left? If so, it sounds like that alarm app is running as a Service rather than registering with the system's AlarmManager.

When you swipe the app away from the multitasking view, you are killing the Service. More details

I have only a few suggestions:


Ensure the app cannot be optimised to save battery. Settings->Battery->Battery Optimisation (Overflow menu). Ensure app is displayed in Not optimised section.
Don't swipe the app to close it. This typically isn't needed on modern Android phones. Though really, I'd still not trust the alarm as the system can clean up apps whenever it needs to.
Use a different alarm app. I use Timely on Marshmallow and have never had a problem with it.