For which purposes is a horn allowed to be used outside built-up areas?

In German traffic rules, outside built-up areas (such as on country roads or highways), the horn is only allowed to be used as a warning signal or as an overtaking signal. This means you should use the horn to warn others of immediate danger (like if a driver is about to miss a stop or if a pedestrian is on the road), or to signal your intention to overtake another vehicle safely.

Using the horn as a calling signal, for example to attract someone's attention generally or to greet others, is not permitted outside built-up areas because it can disturb other road users and does not contribute to traffic safety. Keeping horn use limited to warnings and overtaking helps reduce noise pollution and maintains safety on the road.