Discovery heat detectors have a common profile with ionisation and optical smoke detectors but have a low air flow resistance case made of self-extinguishing white polycarbonate. For the European standard version of the detector, the five modes correspond to five ?classes? as defined in EN 54-5. The classes in this standard correspond with different response behaviour, each of which is designed to be suitable for a range of application temperatures. All modes incorporate ?fixed temperature? response, which is defined in the standard by the ?static response temperature?.