Abstract: The present invention relates to a safety system device for the benefit of cyclists, and in general of all drivers of two and three-wheeled and it can also be used by runners, when they circulate in the streets. The invention comprises a light indicator that is suitable to signal, when a cyclist makes a change of direction, and the rider tries to signal this maneuver by moving outwards the arm corresponding to the side towards which the direction of travel is changing. This device integrates: a lighting element designed to switch on and off according to an appropriate electrical command, an electrical power supply unit, a triaxial accelerometer and an inclinometer sensor. It also comprises calculation means for processing the signals supplied by the triaxial accelerometer and the inclinometer sensor, carrying out an interpretation of the meaning of the movement of the arm.