Correct way to call arbiter

[Alex McFarlane]

Non-frivolous would be:
claims of a draw by repetition or 50 move rule
claims of illegal move
request for promotion piece if not available
making a justifiable complaint about the opponent's behaviour
to seek clarification of the Laws

Of the 5 given reason 1,2 and 3 must be done on your time.
Technically 5 doesn't but I would not be too happy to know that a player had interrupted his opponent's thinking to ask a question on the Laws.
4 would depend on what the opponent was doing and when.