A method to warn of a vehicle moving in the wrong direction of travel, wherein in a provision step, a third-party warning message is provided for other road users when at least one wrong-way-driver signal signals wrong-way travel of the wrongly moving vehicle sensed using a wrong-way-driver sensing method, and in an output step, a self-warning message is output for a driver of the vehicle moving in the wrong direction of travel when the wrong-way-driver signal signals the sensed wrong-way travel and at least one further wrong-way-driver signal signals the wrong-way travel of the wrongly moving vehicle sensed using a further wrong-way-driver sensing method, the further wrong-way-driver sensing method differing from the wrong-way-driver sensing method.