Add me to those to whom "magic words" sounds dismissive and snarky. I have no idea whether that was intended; I'm willing to believe it was not. But in addition to tone, "magic words" has IMO another problem as a description of "players declare actions; DM calls for check if she deems it necessary" - it connotes something constrained/specific, when in fact players declaring actions is just the opposite - very unconstrained. So in addition to the tone problem, it seems to me that "magic words" is just flat inaccurate.
Also, the question heading the poll is ill-phrased for what the poll seems, after subsequent explanations, to be asking. In particular, "if needed" sounds like the context for the question is that somehow it has already been decided that an ability check is in fact needed. In that case, my response would be, "The DM calls for a check." However, given what the poll actually seems to be after, I suggest rephrasing the question as, "When you are DMing, what triggers a player-rolled ability check?"