about the emergency whistle: This emergency whistle is made of high quality aluminum, not easy to rust, firm and durable. It uses high-frequency dual-chamber resonance, and the volume can reach 150dB, and the sound can easily travel far. . Small and Convenient: Our whistle measures 56mm, small and lightweight, and each whistle comes with a key ring that can be carried on a school bag or belt. . Benefits of emergency whistle: This emergency whistle has excellent air circulation design, the surface is anodized to form the color, does not fade, and has a longer service life. And it has no moving parts, no soundproof parts, waterproof, can be used all day, rainy days, wet weather. . Wide Application: The safety whistle is not only suitable for camping, hiking, hunting, fishing, boating and other outdoor activities, but also for sports referees, coaches, schools, dog training, emergency rescue and sporting events. Note: The data is manual measurement, please allow 1-99cm error, due to differences between light and screen, there will be a certain color difference, the specific received in kind shall prevail.