Multifunctional acoustic warning device comprising a movable membrane, a mobile metal core, a fixed core, a coil and a connector which has an encapsulated control system inside, where said control system comprises a pulse generator, an electronic switching device for the disconnection of the coil, a signal processor configured to switch the coil by adjusting parameters of the pulse generator, and an electronic circuit for the measurement of operating variables; the control system having only two connection terminals (T1, T2) for its connection to a vehicle's control unit, such that the acoustic warning device is configured to work in a normal warning mode and in an alarm mode at different frequencies, without the need of additional connection terminals, wherein in case of normal operation of the acoustic warning device, the pulse generator is adjusted by the signal processor to the desired frequency and duty cycle, in order to energise the coil by means of the electronic switching device; and wherein in the event of operation different from normal, the electronic circuit of the acoustic warning device is configured to detect that the acoustic warning device must work in the alarm mode, characterized in that the control system additionally comprises: an A/D converter, for the conversion of an analogue voltage from a disconnected end of the coil to a digital voltage; and that the detecting that the acoustic warning device must work in the alarm mode comprises detecting that it has been activated via the connector by a voltage signal being outside a voltage range specified for said acoustic warning device; and that, depending on the next voltage or pulse train received by the connector through the first terminal in a supply, the pulse generator generates a certain pulse width modulated signal, PWM, producing in turn a certain alarm signal. the control system having only two connection terminals (T1, T2) for its connection to a vehicle's control unit, such that the acoustic warning device is configured to work in a normal warning mode and in an alarm mode at different frequencies, without the need of additional connection terminals, wherein in case of normal operation of the acoustic warning device, the pulse generator is adjusted by the signal processor to the desired frequency and duty cycle, in order to energise the coil by means of the electronic switching device; and wherein in the event of operation different from normal, the electronic circuit of the acoustic warning device is configured to detect that the acoustic warning device must work in the alarm mode, characterized in that the control system additionally comprises: an A/D converter, for the conversion of an analogue voltage from a disconnected end of the coil to a digital voltage; and that the detecting that the acoustic warning device must work in the alarm mode comprises detecting that it has been activated via the connector by a voltage signal being outside a voltage range specified for said acoustic warning device; and that, depending on the next voltage or pulse train received by the connector through the first terminal in a supply, the pulse generator generates a certain pulse width modulated signal, PWM, producing in turn a certain alarm signal. an A/D converter, for the conversion of an analogue voltage from a disconnected end of the coil to a digital voltage; and that the detecting that the acoustic warning device must work in the alarm mode comprises detecting that it has been activated via the connector by a voltage signal being outside a voltage range specified for said acoustic warning device; and that, depending on the next voltage or pulse train received by the connector through the first terminal in a supply, the pulse generator generates a certain pulse width modulated signal, PWM, producing in turn a certain alarm signal.