This unit is perfect for monitoring an entrance or use as an entrance alarm. Uses a Retro-reflective photoelectric sensor system. When the beam is interupted a "ding-dong" sound or optional siren sound will occur. The speaker volume can be adjusted or turned off. When in siren mode, the sounding time is adjustable from 3 to 30 seconds. The range is up to 22 feet or 7 meters. A 9Vdc power adapter is included. All components plug into each other so no hard wiring is required. You get; 1-Retro-reflective photoelectric sensor.1-Reflector. 1-Speaker/electronic chime. 1- 9VDC power adapter. Hardware included: 3 - mounting brackets. 7-screws. 1-drywall Anchor. The sensing range is 22 feet. Total current consumption is 100mA. (Standby current 25mA). Light Source: IR LED. Control Output: NPN open collector (DC 30V, 100mA Max.). Speaker Response Time; 1 sec. for chime (30 sec. for alarm) The alarm time range is adjustable 3~30 seconds. for the alarm. Speaker Output:..Chime/Off/Alarm (Select by switch) Switch selectable chime-off-alarm. MF018