Sony MDRRF920RK 900 MHz Wireless Headphones (Discontinued by Manufacturer) RF wireless headphone system using FM transmission system Up to 150-foot transmission range with manual frequency tuning/reception Lightweight closed-type headphones with 30 mm drive units for deep bass; volume control on headphones; automatic on/off headphone function Self-adjusting headband for precise and comfortable fit Up to 28 hours battery life using 2 AAA batteries; includes 2 NiMH rechargeable batteries with up to 18 hours' use