AXESS HPBT624 Wireless Bluetooth Headphones with Rechargeable Battery & Built-in Mic, Red Bluetooth 2.1 technology for wireless streaming music and a built-in microphone Lightweight, comfortable design for extended listening Built in rechargeable battery, USB charging cable included Works with most smartphones Frequency: 20hz-20kHz, sound output: 2.5mW, Sensitivity: 99dB+/-3dB, operating range: up to 32 feet Connectivity technology : Bluetooth 2.2