This product is suitable for judges, cranes, aerial photographers, videographers and other places that require full duplex operation.   Features: It can be used as cell phone device for hands-free Bluetooth headset.  Support four referees at the same time full-duplex calls, up to 1000 meters speech range.  Bluetooth 3.0 professional chip, 850mAh battery, talk time up to 8 hours, standby time 240 hours.  The advanced DSP noise suppression technology helps clear music and ensures almost no interference to intercom.  Water resistant IP65, full weather protection.   Specifications: Item type: Intercom;  Chip: CSR BC5;  Quantity: 1PC, 2PCS(optional);  Bluetooth version: 3.0;  Working voltage: 3.3V-4.2V;  The speaker power: 0.25W;  Operating temperature range: -10℃~+45℃;  Radio band: FM87.5~108MHz;  Stand-by time: Approx. 150H;  Charging time: Approx. 2.5H;  Package weight: 1PC: 187g / 6.59ounces;  2PCS: 309g / 10.8ounces;  Package size: 1PC: 165 * 100 * 50mm / 6.49 * 3.93 * 1.96inches;  2PCS: 225 * 100 * 50mm / 8.85 * 3.93 * 1.96inches;   Package list: 2 * Intercom;  2 * Headphone;  2 * USB cable;  2 * Arm bag;  1 * User manual