The ComfilePi has a built-in Piezo buzzer. By default, it beeps when the screen is touched.

To disable the touch beep, simply execute the following commands:

sudo systemctl stop touch-beep.service
sudo systemctl disable touch-beep.service

To enable the touch beep, simply execute the following commands:

sudo systemctl enable touch-beep.service
sudo systemctl start touch-beep.service

The piezo buzzer is tied to GPIO pin 30. One way to program it is to use the pigpio library. For example to play a beep in C++:

#include <pigpiod_if2.h>
#include <thread>
 
using namespace std;
 
#define PIN 30
 
void play_beep()
{
   auto instance = pigpio_start(NULL, NULL);
 
   // We actually can't achieve 2700Hz due to the sampling
   // rate, but it will do the best it can
   set_PWM_frequency(instance, PIN, 2700);
 
   // 128/255 = 50% duty
   set_PWM_dutycycle(instance, PIN, 128);
 
   // play beep for 100 milliseconds
   this_thread::sleep_for(chrono::milliseconds(100));
 
   // turn off beep
   set_PWM_dutycycle(instance, PIN, 0);
 
   pigpio_stop(instance);
}

import time
import pigpio
 
PIN = 30
 
pi = pigpio.pi()
 
# We actually can't achieve 2700Hz due to the sampling
# rate, but it will do the best it can
pi.set_PWM_frequency(PIN, 2700)
 
# 128/255 = 50% duty
pi.set_PWM_dutycycle(PIN, 128)
 
# play beep for 100 milliseconds
time.sleep(1)
 
#turn off beep
pi.set_PWM_dutycycle(PIN, 0)
 
pi.stop()