Gray Ghost Wireless Headphones for Minelab FBS/GPX/GPZ Metal Detector GG-M-WHP Instant response time to targets. 10 hours continuous operation. Dual charger charges both the headphones and transmitter. Full range volume control. Comfortable padded earphones insulates from ambient noise. Specifications:Operation frequency: 2.4GHzAutomatic pairing between transmitter and receiver upon power on.Lithium battery (both transmitter and receiver)Continuous operating time: 10 hoursCharging time: up to 4 hoursTransmission delay: 12.5msTransmitting distance: (between transmitter and receiver) : 20 feetFrequency modulation method: GFSKTransmission power: 4 dBmFrequency response: 20Hz to 20KHz (CD quality)Maximum Volume: 80-85dBDistortion: Operation voltage: 3.1VDC to 4.2VDCOperating current: