Title text:
With a good battery, the device can easily last for 5 or 10 years, although the walls probably won't.
Transcript:
[A loud sound appears out of nowhere in the upper left part of the panel, around the word are many small lines going away from it and before the word there is a warning emoji. In the lower right corner Cueball is sitting in an office chair at his desk in front of his computer. He is holding his hands to his head and begins by shouting and then talking.]
⚠ Boop!
Cueball: Aaaaa!
Cueball: I heard it again!
Cueball: Where is that coming from!?
[Caption below the panel:]
It turns out living well is only the second best revenge. The best revenge is making a tiny hole in someone's wall and dropping in a battery-powered capsule that, every 6-12 hours, plays the alert sound of a USB device connecting.
Source: https://xkcd.com/3100/
I forget where I heard the idea from, but I remember someone coming up with a similar idea, just way more sinister. Basically you get a bunch of these really cheap, battery operated speakers like they mention in the comic, but you put sounds on them like creepy children laughing or ghostly noises that are juuuuust loud enough to hear. Set them to have very long timers at random intervals, and scatter them inside someone's air vents
Back when they were cool ThinkGeek would sell the Annoy-o-tron, which just randomly made a loud beep.
They also had one that made creepy sounds. I had one set to a child laughing in the air vents in a creepy hallway with flickering lights in an old church building.
It was awesome.
Pretty sure I have one of these kicking around somewhere