1 - A device for protection by means of electromechanical relay, comprising: - an electromechanical relay, having a magnetic circuit in which a magnetic field is generated by a control coil when an electric current supplied over one of the electrical input terminals of said control coil flows through the latter, and having a contact power circuit that is movable under the effect of said magnetic field so as to be normally open when the control coil is not being supplied with power and to close when the control coil is supplied with power at a voltage higher than a switch-on voltage, said contact being electrically connected in series between a relay input and a relay output, the relay input being intended to be connected to a DC power source and the relay output being intended to be connected so as to supply power to an electronic control module to be protected; - a coil control device, connected so as to supply power to the control coil at at least one predetermined average voltage (V1, V2) lower than the voltage of the DC power source; - the coil control device is arranged to deliver, to the control coil, a first predetermined average voltage that is higher than the switch-on voltage of the electromechanical relay during an engagement step with a predefined duration after the coil control device has been supplied with power from the DC power source; - the coil control device is arranged to deliver, to the control coil, a second predetermined average voltage that is not much higher than a switch-off voltage of the electromechanical relay after the engagement step, and to maintain said second predetermined average voltage for as long as the coil control device is being supplied with power from the DC power source; - the coil control device is arranged to prevent the control coil from being supplied with power while the coil control device is not being supplied with power; - the coil control device comprises an electronic switch that is driven, via an interface, by a control voltage generator, wherein: - the coil control device is a pulse-width-modulation voltage-switching device; - the control coil is connected on one side to the relay input via said electronic switch of the coil control device, and is connected on the other side to a common ground via a master switch outside the device for protection by means of electromechanical relay; - the control voltage generator is supplied with power between the common ground and the relay output, such that it is supplied with power and operational only when said contact of the electromechanical relay is closed; - the electronic switch is arranged so as to be in the closed state when the master switch is closed and in the absence of a signal received from the control voltage generator, and to be in the open state in the presence of a signal received from the control voltage generator. - an electromechanical relay, having a magnetic circuit in which a magnetic field is generated by a control coil when an electric current supplied over one of the electrical input terminals of said control coil flows through the latter, and having a contact power circuit that is movable under the effect of said magnetic field so as to be normally open when the control coil is not being supplied with power and to close when the control coil is supplied with power at a voltage higher than a switch-on voltage, said contact being electrically connected in series between a relay input and a relay output, the relay input being intended to be connected to a DC power source and the relay output being intended to be connected so as to supply power to an electronic control module to be protected; - a coil control device, connected so as to supply power to the control coil at at least one predetermined average voltage (V1, V2) lower than the voltage of the DC power source; - the coil control device is arranged to deliver, to the control coil, a first predetermined average voltage that is higher than the switch-on voltage of the electromechanical relay during an engagement step with a predefined duration after the coil control device has been supplied with power from the DC power source; - the coil control device is arranged to deliver, to the control coil, a second predetermined average voltage that is not much higher than a switch-off voltage of the electromechanical relay after the engagement step, and to maintain said second predetermined average voltage for as long as the coil control device is being supplied with power from the DC power source; - the coil control device is arranged to prevent the control coil from being supplied with power while the coil control device is not being supplied with power; - the coil control device comprises an electronic switch that is driven, via an interface, by a control voltage generator, - the coil control device is a pulse-width-modulation voltage-switching device; - the control coil is connected on one side to the relay input via said electronic switch of the coil control device, and is connected on the other side to a common ground via a master switch outside the device for protection by means of electromechanical relay; - the control voltage generator is supplied with power between the common ground and the relay output, such that it is supplied with power and operational only when said contact of the electromechanical relay is closed; - the electronic switch is arranged so as to be in the closed state when the master switch is closed and in the absence of a signal received from the control voltage generator, and to be in the open state in the presence of a signal received from the control voltage generator.