At low OPL, a player is not required to notify other players of triggered abilities when they are not the accountable player, but it is encouraged for sportsmanship and learning.
§ 506.2.a Tournament Rules PDF (officieel)
§ 506 Triggered Abilities
§ 506.2 Players are not required to notify other players of triggered abilities when they are not the accountable player, but may if they wish.
