This was a project I did wayyyy back in 2020 that isn't strickly ZOE related but I counted it anyways.
Two 555 timers, one modulating the other, connected to a speaker and soldered together on perf board. Powered with a battery too.
I was able to bring it over to a friends house and demo it live. I also brought it to work to share with co-workers. It's been sat in my electronics junk pile since.
Maybe someday I'll add schematics and photos of it. For now, this is the only acknowledgement of its existence.