The Cobalt allows complete wireless freedom plus the Full Sound of Koss. The Cobalt uses frequency hopping technology for interface-free audio. 30-foot range allows you to move freely while taking a call or listening to your favorite music or movies. The Cobalt is also sold with a USB dongle transmitter, allowing you to plug into your computer. The Cobalt has an approximate battery life of 8 hours. It can be used with your computer, CD, DVD, or MP3 Player and with select mobile phones. Behind-the-head design provides maximum comfort and foam ear cushions allow for hear-through sound.