Comment by tripzilch

I actually did this, sort of.

It was to scare away the stone marter family that had made themselves a home under my parents' roof tiles. They are a protected animal where I live, so you can't just do anything to get rid of them. But they also tend to chew on cables in your car (they really do), making them dangerous. Also make a LOT of noise when they go hunting at night.

Looking up various ways to get rid of these animals (apparently they also really dislike the smell of toilet fresheners, which you can place under your car hood or something), I found an ultrasound device but it was kinda expensive for single use.

So I generated a bunch of high frequency tones, to make it extra annoying I had it do random(10,20) seconds of beep, then random(10,20) seconds of silence.

I burned this to a CD, made three tracks at 15kHz, 17kHz and 19kHz. I didn't go higher because I had no way to find out if the speakers would be able to reproduce that tone :) I could clearly hear 15k, and my parents a little. I could nearly hear 17k, and my parents swore they heard nothing. Neither of us could hear the 19k, even at the loudest volume.

Since I don't live there, we decided to put the 17k track on repeat, at max volume, because at least we knew it made a sound (that I could barely hear). The CD player was placed next to an open window close to the nest.

That very night, the stone marter family got up and left. We assumed they probably just moved a few houses over, or something. However ...

Just to be sure they wouldn't return, my parents left the CD player on repeat for an entire week. After that week when my dad turned off the CD, five minutes later, he walked into the garden ...

"Hey, the birds are back!"

(... and to think there's a popular route close to their house for people walking their dogs ...)

So yeah, that definitely worked. It's just not very specific :-P