BioShock Infinite - Boy of Silence

The Boys of Silence are the alarm equivalent of a Security Camera in Columbia. Wearing a blue suit, and blind by his large helmet, he's able to detect Booker via large funnel-like horns that increase his hearing.

The player must choose whether to sneak by one or engage in combat, which triggers a Boy of Silence to open the mouth of his helmet and emit an alarming screech to alert nearby enemies.