Long-range acoustic devices (LRADs) were developed by American Technology Corporation, and are capable of emitting a maximum volume of 151 decibels (that's super loud), within 30 degrees of where the device is pointing. That sort of volume is loud enough to be painful and may cause permanent hearing damage. The LRAD's highly directional sound reduces the risk of exposing bystanders to harmful audio levels.
At lower volume, LRADs can be used as high-powered speakers, "to communicate effectively to large public gatherings, in search and rescue operations, and to defuse deadly SWAT situations." ATC claims LRADS are vastly superior to megaphones or vehicle speakers. Even so, don't expect a product review from me anytime soon!
ATC initially sold LRADs primarily to the U.S. military, but has since sold its products internationally and domestically.