AX-500PLUS. Built to take the worst. With over 14kV surge protection, impact resistant covers, and more than 99% beam tolerance, these detectors withstand the most severe environmental conditions. Extra large dual beams are used to provide the greatest protection against false alarms caused by birds, falling leaves, and other disturbances. These beams have everything you need for a quality installation, including a form C relay and Conduit knockouts, as well as optional heaters, back covers, and beam towers.