I legitimately own a number of actual mad scientist revenge devices. These are small gadgets that can do things like shoot arcs of electricity, a
220db 160db alarm that can deafen, a set of inductors that can generate enough vibrations to crack walls and glass. Also I own Bear Mace.
But by far, the most devious device in my arsenal is a tiny little speaker that emits a super high pitch frequency just barely audible by humans. I can adjust the frequency so it's just high enough that I can't hear it but anyone younger than me can. And the sound is EXCRUCIATING! What's more you can't tell where the sound is coming from. When ever I've played the sound for someone they insist I never do it again.
My wife and I are moving. We've had enough of a local business that moved next to us and became a popular hangout for under-40s. They smoke and drink and hoot and holler.
So I have deployed the device. It is currently running. It's early yet but the drunkies will start showing up over the next few hours. I just wish I had set up a microphone to record their comments, but I will have to just sit here and have a smug knowing a bunch of Millenials will be getting headaches for weeks, until the battery dies. Note: I put in a fresh battery. I will not be retrieving the device. Free gift to the "entitled" generation.