Quote Originally Posted by Chronos View Post
A 98 contention:

If the guard was not aware of the rogue before, then on a tie (where nothing changes), he would remain unaware of the rogue. The check should be rolled at the point when the rogue could have become noticeable, and so, before the check, the rogue was not noticeable.
R98: You make a good point: “Both participants in a contest make ability checks appropriate to their efforts. They apply all appropriate bonuses and penalties, but instead of comparing the total to a DC, they compare the totals of their two checks. The participant with the higher check total wins the contest. That character or monster either succeeds at the action or prevents the other one from succeeding.

If the contest results in a tie, the situation remains the same as it was before the contest. Thus, one contestant might win the contest by default. If two characters tie in a contest to snatch a ring off the floor, neither character grabs it. In a contest between a monster trying to open a door and an adventurer trying to keep the door closed, a tie means that the door remains shut.”

My example was focused on the situation (first example), yours on the guard being perceptive (second example).

I think this may be a case where the DM must decide which example to use.