A detection unit, part of the system, is placed at a considerable distance from the location where the work is carried out. When this unit detects a train approaching, it notifies the workers on the tracks by means of light and acoustic signals, generated by a unit located at the work site. This unit measures the ambient noise and adjusts its alarm volume accordingly.
This system enables certain activities to be carried out in the daytime and outside the weekends, for example doing measurements, carrying out minor repairs and adjusting points.