The device (1, 2) according to the invention concerns a regulator comprising a circuit (1) generating an activation command (KEY_ON) for activating the regulator by bringing, to a first voltage higher than a high reference voltage, a bidirectional line (6) connected to a detection circuit for detecting a status of the activation command. The detection circuit comprises generation means (7, 9) for generating a fault signal from a flag (LAMP_ON) indicating a failure of the alternator, linking the line to a ground by means of a switching element (7), thus bringing the line (6) to a second voltage lower than a fault voltage lower than the high reference voltage, and the control circuit (1) comprises detection means (4) for detecting the fault signal. According to the invention, the control circuit further transmits a setpoint PWM signal having a maximum higher than the high reference voltage and a minimum lower than a low reference voltage higher than the fault voltage, a duty ratio of the setpoint signal being representative of a setpoint voltage (V0) of the regulator.