The invention relates to a safety system 10 for motor-driven vehicles 12 comprising at least one door 14. The system 10 comprises a movement detector 161, . . . , 16N at each door 14 to detect movement within a predetermined area 181, . . . , 18N near said door 14 and/or a movement detector 20 at the rear of the vehicle 12 to detect movement within a predetermined area 22 behind the vehicle 12, and wherein each movement detector 161, . . . , 16N, 20 is also connected to an indicator 261, . . . , 26N, 26B arranged in conjunction with the driver's seat 24 in the vehicle 12 in order to attract the attention of the driver upon detection of movement within said area/areas 181, . . . , 18N, 22.