Compound horns, powerful and crisp voice, fan-shaped sound transmission, and battery saving. Use imported manganese steel sound board, which can keep clear and powerful sound at all times in different environments. It gives a strong sound with smaller and lighter design. Unique waterproof buckler design to get best waterproof performance. Excellent original equipment standards, working on temperature range of -40 degrees to +80 degrees, and can whistle for three minutes. High quality material can prevent salt, resist the hit of sand and stone fragments. Be able to adapt to all kinds of weather.