1. Whistle original mouthguard, prolong the service life. ABS resin strengthened whistle mouth, stable and chewy.2. Applicable to various scenarios, basketball, football, volleyball games, traffic guidance, military training and so on.3. High frequency boom, lightweight and portable. Considering that human ears are more sensitive to the of 1000‑4000Hz, the treble frequency is set to 4000Hz.4. Adjustable nylon hanger, hanger easily through the tail hole, double ball fixed hanger length, not afraid of losing, not afraid of falling.5. Two independent sound holes. In a volleyball match, the referee is located in the middle of the court. The professional volleyball referee whistle, and the sound can be transmitted to both sides.Spec:Item Type: Referee WhistleMaterial: ABS ResinFrequency: 0-4000HzWeight: Approx.30g/1.1ozProduct Size: Approx. 49x20x13mm/1.9x0.8x0.5inpacking list:1 x Whistle1 x Lanyard2 x Mouthguard.