The inspiration for this circuit came from one of those
doorbells that played the same tedious repertoire (eight tunes) over and over
again. Why not, I thought, design a doorbell that would play an infinite variety
of notes? Thus the idea for a random doorbell was born. But while the circuit
described here will play about 20 million different sequences of notes on a
single setting - most of them never previously combined, few people would
actually want to use it as a doorbell, unless they were utterly tone-deaf.
It sounds pretty horrible, let me tell you.
Which is why this circuit rapidly "morphed" from a doorbell to
a raucous alarm. It's now the alarm you build to get people's attention and
then, because they will hate the sound it makes, they will do whatever is
required to stop the alarm. And isn't that what you want an alarm to