If a given ping object doesn't respond to sent packets ICMP, /usr/bin/david-system/ping-alarm.sh program is run periodically (every 5 minutes by default) by Service of Network Management Map for it. The program executes PHP script /usr/bin/david-system/ping-alarm.php, that causes sending a sound alarm (an audio fle) and sends the message to a serial port (to a file /dev/ttyS0), where you can connect an additional text terminal. If you want to run this functionality, change a value of the variable audible at the end of the PHP script from false to true.