Features: 1) Models: 2-wire, 4-wire 2) Advanced detection and discrimination algorithms 3) Easy installation and maintenance 4) Polished low-profile housing design 5) Durable sensor head, no need for replacement 6) SMD circuit board design: satisfactory quality and reliability guaranteed 7) Integrated heat detector for SD-108-2H and SD-108-4H models 8) N/C (normal / close) and N/O (normal / open) relay output ways for option 9) AR (auto reset) function for security systems (optional for 4-wire models) 10) Sensor base: standard and Schottky Diode style for option 11) Five-year warranty