1)motorcycle skiing helmet headset 2)2000m intercom communication during many people 3)can listen ... easier and safer to communicate. MOTORCYCLE HELMET INTERPHONE HEADSETFeatures descritpion:> RF output power: 0.5W> Frequency point: 410MHz/411MHz/412MHz/413MHz ... cm ( 20 sets , G.W.: 8 KG) This helmet interphone headset is suitable for bikers, traffic police, SWAT, architects, outdoor sports ...