Using a trigger for audio data collection

I am using a combination of a headphone speaker and a special microphone to capture sounds transmitted across a medium. The sounds consist of single tone beeps, and i would like to record only the single tone beeps and not the lack of sound in between beeps, so i would like to set up a frequency trigger so that matlab only captures audio for the duration of the beep. I am using the audiorecorder object right now, does anyone know how to use triggers in matlab? the closest i have come to found is a matlab article called 'Continuous Acquisition Using Analog Input' however i still cannot figure out how to use the triggers toward a specific frequency. The beeps will not last longer then a quarter second, so i need something very fast, not multiple lines of matlab script.

Alternatively, i could record the whole session to a array, and then in post processing remove the audio in between beeps, does anyone know how to filter wav files in matlab to edit out areas that dont include a 20kHz beep?

Thanks for any help