Phone gets stuck on the clock Every once in a while, my phone gets into a weird state where when I press the home or power button, the clock appears (see photo), but it is otherwise "dead": no amount of pressing power, home, or other buttons seems to bring me back to the normal home screen.

I have the impression that maybe the phone enters this state when the battery is very low, but charging the phone does not let it exit this state.

The phone is not completely dead: not only the clock is displayed (and updated), but alarms do ring (and you can snooze or stop them by touching the corresponding button which appears then on the screen).

Any idea what that thing might be (bug or feature?), what might trigger it, and how I can exit this state (other than taking out the battery, which so far has been my only recourse)?

This is a Galaxy S5 running LineageOS-15.1
It turns out it's the "smart cover" feature (the thing that displays time when you close a flip-case-with-a-window), which was misfiring probably because of the presence of a nearby magnet (likely the one in my holster's cover) or some problem in my phone's magnetic sensor.

This feature can be disabled in Settings =&gt; Connected Devices =&gt; Smart Cover.

See the reddit thread where I found my answer.