Duct smoke detector DS is used for discovering early stage of fire in the ventilation ducts. It has optical sensor which ensure fast and reliable fire detection. Device have double sided built-in shortcircuitisloator. These ensure constant loop works, even in case of damage. It also lets you easy find place of that damage. Moreover detectors constantly measures dirtyness level and control units - if needed- shows information about neccesity of their cleening. Dirtyness level is also take to acount of fire detection, makes detection more reliable.