For the last 20 years, you could buy tiny electronic "prank" devices that would emit a shrill beep every five minutes (or some other period). The idea was to hide it in an office or someone's bedroom to torment them. Later models included a light sensor that prevented the device from beeping during the day or when the lights were on. The latest model is designed to beep at random intervals, making it more annoying and harder to find.
I'm not going to link directly to the Etsy store selling them because I think the gadgets are evil. But I'll share what they say about the device:
Ultimate Gag Gift! Annoying PCB beeps at random intervals of 5 to 60 minutes! What better way to convince your friend, relative, or a co-worker they've lost their mind?
Battery Lasts 3 Years – With the included battery you won't have to worry about the fun ending too soon
Super Small, Super Low Profile – Easily hides in cars, photo frames, bedroom nightstand, kitchen cabinets, or behind the TV.
Here are some reviews from happy tormentors:
"I ordered this to prank my grown daughter. I hid it in her room and for several days it drove her bonkers. It was greatness when I finally started laughing and she figured it out…… Highly recommend it for revenge to prankers." — M
"I love it. I snuck it in the car and my wife is terrified something is wrong with her hearing." – R
"I loooove this thing. I bought it to mess with my husband and have been moving it around the house. It is safe to say he's starting to get confused" – S
"Best thing I've bought, my parents are going insane" – T
Oh, what fun!