A safety device for vehicles comprising at least one video camera (2;2a,2b,2c), which has a tilt and zoom function, and which is configured to be installed in a portion of the external rear surface of a vehicle, oriented so that its lens faces in the opposite direction to that of the vehicle 's forward travelling direction, at least one processing unit, to which said video camera (2; 2a, 2b, 2c) is operatively connected, suitable for sending the captured images, selectively and at the request of the driver, to a display of the vehicle, operationally connected to said processing unit by means of wiring or wireless connections, and at least one control, operatively connected to said processing unit, which can be operated by the driver and able to selectively activate said camera (2; 2a, 2b, 2c), and therefore, the rear viewing function on said display, said display being a display already supplied to current vehicles, and it consists of the display of the instrument panel of the vehicle positioned frontally with respect to the driver, said control being configured so as to allow the operating mode to be changed, from the first mode to the second mode, in which the rear view is active, only when the driver actively works on it, so that the driver, only and exclusively when they wish, may decide to instantly change the way in which the display is used to activate the rear view generated by said video cameras (2; 2a, 2b, 2c), said control comprising at least a button, a lever, a knob, or the like, adapted to be located on a steering wheel or a handlebar of the vehicle, on the spokes of the steering wheel, or also in the internal part of the wheel of the steering wheel, or said control being of the vocal type, characterized in that said control is configured to selectively modify, at the discretion of the vehicle's driver, the mode of use of said display from a first mode, wherein the rear viewing function is not active, to a second mode, wherein the rear viewing function is active, and vice versa, and wherein in said first mode of use said display operates like a traditional display, i.e. it shows the normal information relating to the vehicle, and possibly also graphics and/or images, and wherein, in said second mode of use, said display is controlled to display, in real time, the images taken by said video camera (2;2a,2b,2c), said display being able to selectively display the images taken by said video camera (2;2a,2b,2c) when the vehicle moves in the forward direction, engaging the entire surface of the display of the instrument panel to have a larger image installed in a portion of the external rear surface of a vehicle, oriented so that its lens faces in the opposite direction to that of the vehicle 's forward travelling direction, at least one processing unit, to which said video camera (2; 2a, 2b, 2c) is operatively connected, suitable for sending the captured images, selectively and at the request of the driver, to a display of the vehicle, operationally connected to said processing unit by means of wiring or wireless connections, and at least one control, operatively connected to said processing unit, which can be operated by the driver and able to selectively activate said camera (2; 2a, 2b, 2c), and therefore, the rear viewing function on said display, said display being a display already supplied to current vehicles, and it consists of the display of the instrument panel of the vehicle positioned frontally with respect to the driver, said control being configured so as to allow the operating mode to be changed, from the first mode to the second mode, in which the rear view is active, only when the driver actively works on it, so that the driver, only and exclusively when they wish, may decide to instantly change the way in which the display is used to activate the rear view generated by said video cameras (2; 2a, 2b, 2c), said control comprising at least a button, a lever, a knob, or the like, adapted to be located on a steering wheel or a handlebar of the vehicle, on the spokes of the steering wheel, or also in the internal part of the wheel of the steering wheel, or said control being of the vocal type, characterized in that said control is configured to selectively modify, at the discretion of the vehicle's driver, the mode of use of said display from a first mode, wherein the rear viewing function is not active, to a second mode, wherein the rear viewing function is active, and vice versa, and wherein in said first mode of use said display operates like a traditional display, i.e. it shows the normal information relating to the vehicle, and possibly also graphics and/or images, and wherein, in said second mode of use, said display is controlled to display, in real time, the images taken by said video camera (2;2a,2b,2c), said display being able to selectively display the images taken by said video camera (2;2a,2b,2c) when the vehicle moves in the forward direction, engaging the entire surface of the display of the instrument panel to have a larger image