What does “jemanden im Auge behalten” mean in German?

A supermarket owner, convinced a customer might be shoplifting, tails him from aisle to aisle without ever confronting him — she’s keeping him im Auge, literally “in the eye.” Jemanden im Auge behalten means to watch someone or something closely, tracking how a situation develops rather than glancing at it once. It works for people, projects, prices, or symptoms — anything you want to monitor rather than ignore.

The idiom traces back to Luther’s Bible translation, part of a whole family of German eye-related idioms about perception and vigilance. Its close cousin, etwas im Auge haben (“to have something in view/in mind”), is slightly different: it means having something as a goal or plan, not tracking its behavior over time.