Fake ultrasonic people repeller and pest repellent
Have you heard the buzz about ultrasonic technology to repel mosquitos, cats, dogs or even kids? Now you can brag about this supposed technology (not proven really) in your own phone and then beam your friends with a disgusting beam of high frequency sound to prove your point.
Try it outside, maybe some mosquitos and flies may feel repelled by it and you can take credit for it. Hehehe...
While some people may insist that ultrasonic and high frequencies can indeed repell pests and mosquitoes, This technology is not proven to work. But... it is a good prank anyway.
Be careful who do you beam with these frequencies, they may turn out to be extremely annoying. Almost tinitus-like sounding.