AXESS HPBT619 Wireless Bluetooth Over-Ear Headphones for Smartphones with Hands Free Calling, Green Wirelessly stream music with Bluetooth V4.1 from your smartphone Sensitivity microphone and volume control allowing for hands free calling and control user-friendly controls and comfort able ear pads for optimal experience. Built-in 400mAh rechargeable Lithium-ion battery for 10 hours of continuous music playback Receiver distance: up to 20 meters, Frequency response: 20-20kHz Connectivity technology : Bluetooth 4.1