Wake-up call (7,5)
'wake-up call' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for reality check that I've seen before include "Reminder of the true state of affairs" , "Sobering fact" , "Reminder of true conditions" , "Moment to consider things in an honest manner" , "In which one is reminded of things as they are" .)
(Other definitions for alarm that I've seen before include "Warning of danger" , "with which many awake to in the morning" , "Arouse to a sense of danger" , "Tocsin" , "State of (sudden) fear" .)