Outdoor sirens: How do they work for people indoors?

People are normally indoors where the sounds from outdoor warning sirens are greatly attenuated by building structures. Nevertheless, practical experience and the results of tests by the Federal Emergency Management Agency and others have shown that siren sounds are quite effective for alerting large populations—including those indoors. Why is this so? Based upon data in the literature, three possible explanations are examined in this paper: (1) the possibility that the sounds from sirens outdoors, even though attenuated through building structures, are still sufficient to directly alert people indoors; (2) the possibility that people indoors are more responsive to siren sounds than people outdoors; and (3) the possibility that people indoors are alerted by other people who are outdoors when they hear the siren sounds. This examination indicates that all three mechanisms could be contributing to the effectiveness of siren sounds indoors. Their relative significance is not known, but probably varies with geographic location, weather conditions, and time of day.