Historically the Bosun's Whistle, aka the boatswain's call, is used for passing commands to the crew over the daily noise of a operating warship. It's a shrill, high-volume blast of sound to get yourself noticed just about anywhere. The most famous use in popular culture is probably for signaling "open shipboard communications" on a certain classic sci-fi television program. Would work as an excellent emergency safety whistle, just add your own chain and be ready for anything.
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