A system that is implemented in a vehicle (1) having front and rear doors (2) (3) with door opening sensors (SM; SD, SE) and one indicative sensor (ST) of locked door. A processing unit (4) calculates, by measuring the time the door remains open and by the sequence and/or frequency of openings and closings the doors (2, 3), the possibility of a non-self-sufficient occupant have been forgotten inside; and controls the actuation of an alarm (A1, A2, AL) in the event of the calculation indicates the possibility of such occupant have been forgotten inside the vehicle. The system identifies the possibility of an occupant has been introduced inside the vehicle when the opening time of the rear door is longer than time T1, and identifies the possibility of an occupant has been forgotten in the vehicle by means of the information processing sent by the door sensors.