1. A method of monitoring an acoustic environment of a mobile device for voice commands when the mobile device is operating in an idle mode, the mobile device having a first processor and a second processor, the method comprising: receiving acoustic input while the mobile device is operating in the idle mode; performing at least one first processing stage on the acoustic input using the first processor, prior to engaging the second processor to process the acoustic input, to evaluate whether the acoustic input includes a voice command; performing at least one second processing stage on the acoustic input using the second processor to evaluate whether the acoustic input includes a voice command if further processing is needed to determine whether the acoustic input includes a voice command; wherein performing the at least one first processing stage or the at least one second processing stage includes, while the mobile device is operating in the idle mode, transmitting at least a portion of the acoustic input to at least one server via a network for processing by the at least one server at least to evaluate whether the acoustic input includes a voice command; and initiating responding to the voice command when either the at least one first processing stage or the at least one second processing stage determines that the acoustic input includes a voice command.