Motherboard
echo -ne '\007'
echo -e "\a"
echo -n <Ctrl+V> <Ctrl+G>
SSH
$ echo -en "\a" > /dev/tty5
printf "\a"
tput bel
beep
Speakers
play -q -n synth 0.1 sin 880
$ speaker-test -t sine -f 1000 -l 1
$ (speaker-test -t sine -f 1000) & pid=$! ; sleep 0.1s ; kill -9 $pid
paplay /usr/share/sounds/sound-icons/capital
aplay /usr/share/sounds/sound-icons/prompt