The HD 4.40 BT is a wireless headset employing Bluetooth 4.0 and aptX technologies to deliver exceptional wireless Hi Fi sound. It features NFC for simple pairing of compatible devices. This new headset offers ease of use and convenience thanks to intuitive ear cup mounted controls for changing tracks and for making calls via the integrated microphone. Wearing comfort is assured by their ergonomically designed ear pads. The HD 4.40 BT has excellent battery life, letting listeners enjoy wireless sound for up to 25 hours. A battery free listening mode is also possible via a supplied detachable cable. Note for good sound quality and best wearing comfort adjust the ear pad location on the headband to properly match the size of head. Wear the headphones so that the headband runs over the top of your head. Adjust the location of the ear pads by moving the ear cups up and down of the headband slider until ears are comfortably covered by the ear pads, you feel even gentle pressure around your ears a snug fit of the headband on the head is ensured.