Abstract: A device for detecting the unbalance of a rotating machine from a predetermined threshold. This device includes a pendulum formed from a vertical rod made of an elastically deformable metal, the upper end of which is embedded in an insulating support fixed rigidly to the housing of the rotating machine and which at its lower end carries a metallic mass, the mass being received concentrically, with a predetermined peripheral play, within a metal rink likewise fixed to the housing and insulated electrically from the housing, the ring and the embedded end of the pendulum being connected electrically to an electrical alarm or safety circuit which closes as soon as the mass comes in contact with the ring, where the resonance frequency of the pendulum is below that of the parts of the rotating machine which is subjected to the unbalanced condition.