Alarm is an action that starts a loud notification whenever it receives a signal.
When an alarm is on, the notification in the notification bar appears. Alarm can be dismissed either by swiping notification to the right or by clicking it, which will open Dessin and show alarm node, and swiping alarm menu to the right.
When alarm is active, its swipe menu changes. On the left there is an option to dismiss the alarm and return to previous activity. On the right there is an option to dismiss the alarm. Swiping downward will silence the alarm and stop vibrations but it won't remove the notification from the notification bar.
Alarm gets triggered only when it was in the deactivated state and it just received activate message. It means that you should make sure that an alarm node will eventually receive deactivate message in order to reset its state.