I would three main deliverables for this project.
1) A tool that can take an audio file. Lets suggest an WAV or PCM audio. Encode hidden tones into the audio.
2) A software tool that can listen to the audio being played and detect the hidden tones.
3) The programming of the detector software into an Hardware Audio DSP that can listen to the tone and trigger a result such as on off switch on the tone.
More detail please ask questions.