A magnetic-field sensor based on the giant magnetoimpedance phenomenon is presented. It is shown that a low, negative magnetostriction CoFeBSi amorphous wire can be used to detect the presence or passage of moving pieces or vehicles, simply by pasting a small permanent magnet on the vehicles/pieces. The detection is observed as a decrease in the ac voltage on the wire’s ends. A system of such devices can be used to monitor and control a number of industrial processes.