There is a PCB make it Yourself Project that was very low power and played a cricket sound at random intervals. It lasted Years on a coin cell. Don't use this on mentally unstable people!
xkcd
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Alternatives: Discord DM sound, Microsoft Teams notification sound
Grindr notification sound.
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
A cricket sound, on a random interval going up to an hour between.
Edit: FOUND IT! https://lemmy.ca/post/41987749
Back when they were cool ThinkGeek would sell the Annoy-o-tron, which just randomly made a loud beep.
what happened to thinkgeek?
They were bought and basically no longer exist. Hot Topic was going to buy them but then GameStop came in with a higher offer. For a while they launched ThinkGeek retail stores in shopping malls but eventually shut them all down and now they basically only exist as some tchotchkes in GameStop stores. Even the website just seems to redirect to the main GameStop page now, not their “store” within the GameStop webstore.
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.