The Cobalt allows complete wireless freedom plus the full sound of Koss. Going wireless has never been so easy. The Koss Cobalt uses frequency-hopping technology for interface-free audio. Providing a 30-foot range, you can move freely while taking a call, or listening to your favorite music or movies. Just working on your PC. The Cobalt can also be used with select mobile phones, utilizing its built-in microphone. It simultaneously pairs with the phone, allowing users to answer calls with the same headset used for listening to portable music players.