Abstract: A fence having security wires fastened to posts via sensors and having an electronic evaluation circuit connected to the sensors, which releases an alarm signal when one of the sensors signals a contact of the security wire which is connected to it. Each sensor has a housing fastened to a post, a holder connected to a security wire and a transformer placed between housing and holder, which produces a signal which is approximately proportional to the position of the holder. An alarm signal is generated when one or only a few security wires move slowly, yet such slow movements are ignored when caused by environmental factors. A highly reliable security fence is thus obtained.