Upgrade your backpack with Milspec Whistle Side-Release Buckle. This signal whistle is ideal for survivalists, simply attach it to the webbing on your backpack for easy access in times of need. The survival whistle is designed to fit on most standard sized backpack straps (Measures 5/8 inches wide). The secure side-release buckle comes equipped with a durable waterproof composition. This loud whistle is perfect for soldiers, survivalists, campers, or anybody who enjoys the great outdoors.