When I was first introduced to BASIC in elementary school, I was spending a lazy afternoon reading in the built-in QBasic docs (being able to hit F1 and get imm

When I was first introduced to BASIC in elementary school, I was spending a lazy afternoon reading in the built-in QBasic docs (being able to hit F1 and get immediate help is still one of the coolest things ever IMHO) about the SOUND keyword, which let you set a frequency and duration. I remember irritating the hell out of my parents (and our dog) with it until one day, by accident, I noticed they couldn’t hear the tone anymore. The frequency was somewhere in the range of 15-20 kHz IIRC. So I wrote a “PASSWORD.BAS” source that would play that high pitched sound in short, one-tick intervals continuously while polling the keyboard for input but then stop after a random amount of time. To authenticate, the user had to hit the spacebar within a one second window of the sound’s termination. Hitting the spacebar too early would also result in access denied. Fun times!