There is a "beep.vi" on the Graphics and Sound palette.
Call it when you detect the peak.
I usually put the beep code in a subvi that is fed by a queue.
Your implementation will depend on how you want it to work.
Is it a one time beep or does it beep as long as the value is above a limit?
Sorry for that. Here is the sc. You can adjust the duration and frequency of the tone. Details can be found in context help.