A simple buzzer, that can be used to gain human attention.
I’d suggest a “default” of, say, a 1 second beep. It would also have a “turn on” command, and a “turn off” command, and maybe even control to set volume and frequency (tone) of the beep.
If you want to get really fancy, have a mode that it would “beep out” an ASCII character as Morse Code, with programmable code speed.
Nothing complicated – no need to have something as fancy as “trigger” sound board. Just a few beeps.