https://en.wikipedia.org/wiki/Crystal_detector https://en.wikipedia.org/wiki/Crystal_detector for more info :) Fun fact: this is referenced in the book Childre

https://en.wikipedia.org/wiki/Crystal_detector https://en.wikipedia.org/wiki/Crystal_detector for more info :) Fun fact: this is referenced in the book Children of Time! I thought it was a made-up device until I dug in a little and learned it was actually possible