OT: Hey You Weirdos!

[Suicide Junkie]

Have you never hooked up a high frequency signal into a speaker in a tech class?
Pitched high enough that the teacher can't hear it due to age, but some of the students can?

Quite entertaining to watch, but does get on your nerves after only a few minutes; even if you turn it up enough that can't hear it personally.

You could probably introduce an inaudible squeal to a gift radio without adding components if you googled the right things.