The new SL-650QN includes even more features to protect against false and missed alarms caused by mis-alignment and environmental issues. With 650ft. of outdoor detection range, the QN model is perfect for mid level security perimeter applications. New features include:Quad beam - Dramatically cuts down on false alarms caused by birds and falling leaves Sniper ViewFinder and aligmnet dial - The new telescope lens on the SL Series has a high level of visibility for optical alignment work. Even at 650ft., a perfect installation and stable performance can be achieved in minimal time.BAU-4 Compatible - The BAU-4 beam alignment unit automatically and accurately adjusts the optical access. This allows peak performance and gives one technician the ability to align a 200ft to 650ft SL detector without additional help.