Audio headphones are small speakers worn over the ears to isolate sounds for the listener. They use three basic technologies: standard, wireless, and infrared. Standard audio headphones, headsets and ear buds use wires to receive an electrical signal from a transmitter. As the current through an electromagnet varies with the signal, the headphone diaphragm vibrates in response. Wireless headphones are cordless, battery-powered audio headphones which receive radio frequency (RF) signals, typically at 900 MHz. Listeners can travel anywhere within a specified range and still receive audio outputs. Infrared headphones use infrared (IR) light to carry data from a transmitter to a receiver. The transmitted signal is converted to an electrical impulse which drives the speakers in the headset. Unlike wireless headphones, however, IR headsets require listeners to remain within a transmitter’s line of site.