Wireless Bluetooth Over-Ear Headphones pack powerful wireless sound into a portable, fold-flat unit. The Koss BT539i Wireless Bluetooth headphones have the natural fitting, iconic "D-profile" earcup, first featured on the ergonomically designed Koss Pro4AAA and now available on many Koss headphones. The D-profile mimics the shape of the ear, creating an excellent seal for the most consistent sound reproduction. Listeners stay connected using the built-in microphone. Easy to locate, on-board controls allow listeners to quickly navigate through songs, play or pause music, change the volume level, and answer incoming calls. The built-in rechargeable lithium-ion battery delivers up to 12 hours of play time or 12 hours of call time (at moderate levels) and 40 hours of standby time on a single charge. If the rechargeable battery runs out, the BT539i comes with a detachable analog cord, which can be used as an audio bypass. Closed ear cushions fit comfortably around the ears to block outside noise and keep music from leaking out. Finish: Black.