System to be installed on a helmet composed of an electronic control unit, that is an electronic board surrounded by its case on which at least the following minimum components are installed: - a microprocessor, - a GPS receiver, - a dedicated battery, - a mobile communication unit, - an inertial tridimensional gyroscope, - accelerometers, - one push button for manual activation of the emergency call, - one wireless receiver, and composed of external accelerometers, an external microphone, and an external loudspeaker mechanically and electrically connected to the electronic control unit, characterised in that: - The system is to be installed on a helmet closure strap and it is composed of the flexible electronic control unit, that is an electronic board surrounded by its case and made of flexible material, on which at least the following minimum components are installed: - two microprocessors, - two GPS receivers, - two dedicated batteries, - two mobile communication units, - two inertial tridimensional gyroscopes, - two bidimensional accelerometers with the X axis along the longitudinal direction and the Z axis towards the ceiling, - two blood pressure sensors, - two electrical outputs with attached wires for microphones, and composed of at least two external loudspeakers (631, 633) mechanically and electrically connected to the electronic control unit; - Two sets of three external accelerometers (631, 632, 633) are connected to the electronic control unit and positioned inside the helmet, with two sensors placed on the nape of the neck of the user; - The case surrounding the electronic board is flexible, its size is comparable with the helmet closure strap and it has at least two openings on one of its baseplates through which the strap shall be inserted and no structural discontinuity is present; the case is connected on one side to the helmet lock, that is to say the component which closes the helmet strap, and on the opposite side to a semicircular ring to be installed inside the helmet as mechanical support for external accelerometers, for a microphone, and for loudspeakers connected to the electronic control unit; - Two blood pressure sensors are placed into contact with the user's skin, when the user wears the helmet. - a microprocessor, - a GPS receiver, - a dedicated battery, - a mobile communication unit, - an inertial tridimensional gyroscope, - accelerometers, - one push button for manual activation of the emergency call, - one wireless receiver, - The system is to be installed on a helmet closure strap and it is composed of the flexible electronic control unit, that is an electronic board surrounded by its case and made of flexible material, on which at least the following minimum components are installed: - two microprocessors, - two GPS receivers, - two dedicated batteries, - two mobile communication units, - two inertial tridimensional gyroscopes, - two bidimensional accelerometers with the X axis along the longitudinal direction and the Z axis towards the ceiling, - two blood pressure sensors, - two electrical outputs with attached wires for microphones, and composed of at least two external loudspeakers (631, 633) mechanically and electrically connected to the electronic control unit; - two microprocessors, - two GPS receivers, - two dedicated batteries, - two mobile communication units, - two inertial tridimensional gyroscopes, - two bidimensional accelerometers with the X axis along the longitudinal direction and the Z axis towards the ceiling, - two blood pressure sensors, - two electrical outputs with attached wires for microphones, and composed of at least two external loudspeakers (631, 633) mechanically and electrically connected to the electronic control unit; - Two sets of three external accelerometers (631, 632, 633) are connected to the electronic control unit and positioned inside the helmet, with two sensors placed on the nape of the neck of the user; - The case surrounding the electronic board is flexible, its size is comparable with the helmet closure strap and it has at least two openings on one of its baseplates through which the strap shall be inserted and no structural discontinuity is present; the case is connected on one side to the helmet lock, that is to say the component which closes the helmet strap, and on the opposite side to a semicircular ring to be installed inside the helmet as mechanical support for external accelerometers, for a microphone, and for loudspeakers connected to the electronic control unit; - Two blood pressure sensors are placed into contact with the user's skin, when the user wears the helmet.