Low-frequency sound aimed at birds as they approach busy flight paths could reduce bird strikes that put airliners and passengers at risk, U.S. researchers say. While noisemakers are often used to scare birds away from airport runways, the loud sounds are also a source of annoyance to people within earshot, something the new technology can avoid, they said. Technology International, based in Louisiana, says its system will use infrasound, below the range of human hearing, directed at flocks of birds as they approach airliners taking off or landing. Dubbed the Avian Infrasound Non-lethal Denial System, the technology used a passive infrasound detector that listens for an approaching flock and activates subwoofer speakers that generate high-intensity but low-frequency sound. The system has worked well in tests, NewScientist.com reported. Technology International head Abdo Husseiny said the system could also serve to keep pigeons away from public squares and city parks or divert flocks of birds away from wind turbines