These rust-free and durable safety whistle are made of high quality aluminum alloy, strong and durable, and the light weight is easy to carry around. The sound of these survival whistles is loud and can travel a long distance. A little air is needed to produce the sound. The faster you blow, the louder the sound and the farther it travels, which is best for outdoor emergency supply, referee, coaches, training, sports. Improve your marketing campaign with this colorful and customizable.