An apparatus/vehicle for warning a driver of a vehicle or vehicle/trailer (V-VT) about a stationary object (SO): a) a sensor device having a detection area (DA) including a side DA arranged laterally from a vehicle side (VS) and extending front to rear, in the direction of a longitudinal centerline of the (V-VT), and detecting the SO within the DA; b) a control device to evaluate the sensor signals as to the SO detected within the DA and define a dynamically alterable warning area (WA) that is no more than the side DA; c) a warning device to generate a warning signal if the sensor device detects the object(s) in the WA; d) the control device, on detection of the SO within the side DA and on detection of the (V-VT) turning toward the VS on which the side DA is situated, to assign a triangular cross-section to the WA.