RF/Low Battery Indicator, GREEN indicates Receiver and Transmitter ON and receiving RF. RED indicates Low Batteries * Earphone jack * Audio output control and On/Off switch Left turn for output level decrease, right turn for output level increase * The AS-900 system is a fixed frequency system, but is available with the following frequencies: Code K1: 630.2MHz Code K2: 633.4MHz Code K7: 650.2MHz Code K8: 659.0MHz