The FireGuard detects emerging fires already at their early stages (cold smoke). The sensor uses the available natural air stream in the tunnel. Any influence caused by fog will be eliminated by optional heating elements. The sensor is very compact and has neither movable parts nor wear parts nor does it need consumables. As a light source, an economical LED is used. An adjustable bracket allows mounting at the wall, in the arched section or at the ceiling. Special models for installation in the intermediate ceiling or directly in the ventilation dampers are available. Various ways of connections allow a flexible system integration. Individual setting of parameters allows an optimal object and location related setting of alarms, there are no false alarms. Maintenance is limited to occasional cleaning and the automatic adjustment with a control rod. Soiling monitoring provides information on the state of the instrument. Maintenance is only necessary when required, from experience only about every 5 years, and the time required per instrument is normally between 15 and 25 minutes at the most.