2 Beams IR barriers. Range: Up to 20m outdoor/ 40m indoor. 4 Frequency channel. Provides AND (Y) shot it requires that its beams must be blocked simultaneously to activate the alarm. Bird flight, insects or leaves fall can obstruct one beam but doesn´t activate the alarm of the unit. Offers 4 beams frequencies to avoid mutual interferences (Cross-talk) in linear installations which disposes of 2 alarm zones or in 2, 3 or 4 (max) stecked sensors.