... by single hand4. Strong loudness same effect as traditional whistle.5. Special design metal-tubing to reach 125dB +/-5dB ... threat to persons exists.9. Multi-propose use suitable for: Referee, Coaches, Traveler, Adventurer, Tour Guides, Cheerleaders, Lifeguards, Teachers ... pedometer,heart rate monitor,stopwatch,radio controlled watch,electronic whistle,robot... You can trust our ability,if you product ...