an external speaker into to the speaker port of the computer ala vhf
Hard: Modify source code to, for example, activate a line on a parallel port or trigger an output on an i/o card, etc that connects to a beeper.
Really hard: build a bandpass filter incorporated into external speakers for the computer that detects a particular monotone fixed frequency for a minimum length of time. Once this frequency is detected for a certain length of time minimum activate an alarm
. Set AIS
alarm sound to the monotone fixed frequency and voila!