using to audio out?

I have a project where I use audio in a public space. The user is in a small telephone box talking and needs to hear at the end of his recording an audio signal (the glass warning from apple). The speakers are used for the broadcasting part but the visual artist wants to put a small speaker inside the cabin to notify the user that the recrding finished. This speaker needs to be always on, the public speakers not. How should I solve this?