1. A warning device ( 50 ) in the form of a rear-view mirror for mounting onto a vehicle, in order to attract the attention of the driver when an object is located in a position that is wholly or partially critical for the driver, whereby the device ( 50 ) comprises at least one source ( 5, 6 ) of electromagnetic radiation or ultrasound and an arranged position-sensitive radiation- or sound detector ( 7 ), whereby the source ( 5, 6 ) and the detector are part of an electronic circuit ( 52 ), whereby the detector ( 7 ) detects the presence of an object in a position that is critical for the driver, whereby an output ( 56 ) from the circuit for a first signal with the status of a warning is activated, and whereby a first level ( 54 ) warning signal is given, characterized in that the electronic circuit ( 52 ) of the warning device ( 50 ) comprises the following sensor means with their associated outputs ( 56 ) for activation of a signal with the status of a warning: sensor means for detection of an input signal on/off ( 58 ) from the direction indicators of the vehicle; output ( 56 ) in the circuit for activation of a signal with the status of a warning when the input signal of the direction indicator is on; sensor means ( 60 ) that detect an angular deviation of one of the wheels of the vehicle; output ( 56 ) in the circuit for activation of a signal with the status of a warning when the warning signal is emitted for deviation of the angle; means ( 62 ) for determining the speed of the vehicle; threshold detection means for speeds, whereby predetermined threshold values of speed emit a signal with the status of a warning in combination with input signals from sensor means ( 58, 60 ) in the direction of motion of the vehicle depending on the detection of at least one sensor means ( 58, 60 ); and threshold detection means for a maximum allowed angular deviation in order for the warning device to be active, which indicates rounding of a curve or normal turning of the vehicle.