SD-108 series photoelectric smoke / heat detectors are designed in compliance with the UL-217, prEN-14604 and BS 5446 standards. SD-218 series alarms can be used as smoke sensors and 135-degree Fahrenheit heat detectors. Features: 1) Photoelectric sensing technology 2) Low-sensitivity warning 3) Low-battery warning 4) Polished low-profile housing design 5) Battery case on the back of the detector for easy removal 6) SMD circuit board design: satisfactory quality and reliability guaranteed 7) Test button for battery and alarm operation verification 8) Loud alarm signal exceeding 85dB in alarm mode 9) Easy installation and maintenance 10) Five-year warranty