A safety device for an electrical installation, said device comprising: - electrical contacts suitable to be automatically opened and manually closed in order to disconnect/connect the installation from/to a network power line; - automatic release means that can be actuated in consequence of a failure condition detection in the installation in order to command the automatic opening of said contacts and disconnect the installation from the power line; - control means for performing measurements on the installation by discriminating the nature of the failure condition, said control means being able to act on the release means in order to hold the device contacts opened and prevent the same from being manually re-closed upon a failure condition of a permanent type, said control means comprising a control electronic device that can be electrically connected to the electrical installation and the power line and such as to generate actuating signals for the release means, said control electronic device further comprises: - an electronic check block to carry out measurements of electrical parameters of said installation; - an electronic central block to compare data corresponding to said electrical parameters with reference values and generate the actuating signals of the release means based on the results of this comparison, when the measurements carried out by the check block give out of standard values, a permanent failure is present in the electrical installation and the control device signals the presence of this permanent failure by means of a light signal activating a suitable light LEDs that are provided on an outer envelope of the safety device, characterised in that the safety device, in addition to the light signal, provides a sound signal in order to warn the user that a permanent failure is present in the electrical installation, the sound signal can be silenced either by acting on a push-button that is provided on the envelope of the safety device or by remedying the failure condition, whereby in the latter case the sound signal can be used to locate a failure in the electrical installation by disconnecting the plugs of user loads until the cause of the failure has been identified by the sound signal turning off. - electrical contacts suitable to be automatically opened and manually closed in order to disconnect/connect the installation from/to a network power line; - automatic release means that can be actuated in consequence of a failure condition detection in the installation in order to command the automatic opening of said contacts and disconnect the installation from the power line; - control means for performing measurements on the installation by discriminating the nature of the failure condition, said control means being able to act on the release means in order to hold the device contacts opened and prevent the same from being manually re-closed upon a failure condition of a permanent type, said control means comprising a control electronic device that can be electrically connected to the electrical installation and the power line and such as to generate actuating signals for the release means, - an electronic check block to carry out measurements of electrical parameters of said installation; - an electronic central block to compare data corresponding to said electrical parameters with reference values and generate the actuating signals of the release means based on the results of this comparison,