The present invention refers to a method and a device for confirmation automatically of the state of tightness of fastenings of railroad tracks, so that from a train that is traveling over a track it is possible to detect a signal from each of the fastenings which indicates if the degree of tightness of said fastenings is sufficient or if on the contrary the fastening is deficient because it is either loose or damaged. For this a device object of the invention comprises a pressure sensor element and at least one electrically conducting element connected to said pressure sensor, whereby a variation is produced of at least one electric magnitude proportional to the pressure of tightness present in at least one point in said fastening during the passage of a train. The invention also relates to an insulating plate for fastenings and to railroad track plant, which incorporate a sensor device object of the invention.