US Patent 8204553 Display control for cellular phone

A control system for a mobile device comprises an audio input that generates an audio input signal. An audio amplifier amplifies the audio input signal using a gain. An adaptive gain control (AGC) module receives the audio input signal and adjusts the gain of the audio input signal. A comparing module generates a first signal when the gain is less than a threshold. A timing module determines a duration of the first signal. A selecting module communicates with the timing module and selects one of an active mode and an inactive mode of the mobile device when the duration is greater than a first period.