features and functions 1. Advanced photoelectric smoke sensing technology 2. Durable sensor head; excellent smoke access 3. Ar (auto reset) function for security systems,(optional for 4 wire models) 4. Both n/c (normal/close)-n/o (normal/open) relay dry contact output 5. Easy installation and maintenance 6. Modern design (white and beige colors) 7. Five-year limited warranty 8. Alarm freq. :3~5 SEC. 9. Comply with en54 and CE