RCA WHP141B 900MHZ Wireless Stereo Headphones Transmits audio signal up to 150 feet, through walls, floors and ceilings Phase-Lock Loop (PLL) technology locks in frequency to prevent signal loss 40mm speakers for outstanding sound performance. 900 MHz transmitting frequency 3-channel selection on headphones and transmitter for easy tuning Headphones charge on transmitter for easy storage and use Includes base/transmitter, headphones, batteries, and power supply Compact, comfortable design provides full, rich sound without the bulkiness of most other full-size headphones Three selectable operating channels for reduced interference Transmitter serves as a charging stand (cable charging) Compatible with almost any audio source, such as DVD, CD, DBS or HDTV