Building a bluetooth buzzer
Communication devices that have a built-in GPIO bank typically include the ability to control those pins through whichever protocol they use to interface with the outside world. According to the datasheet for the HM-10 you just use standard AT commands.

On pages 9 and 10:


  
  Query/Set PIO pins output high or low (...)
  
  
  AT+PIO [pin number] ? to query;
  AT+PIO [pin number] [0 or 1] to set low or high.