Infrared-sensors detect the infrared radiation emitted by hot materials and transform it into an electrical signal. Built-in optics to narrow the field of view, combined with a predetermined switching temperature, provide for a wide range of applications. These include precise location and positioning of hot objects in, for example, steel and rolling mills, forges and foundries, and glass and ceramic installations. Hot parts can be tracked over distances of several metres, flames monitored, or mould part removal of hot objects checked.