You can get a red laser diode pretty cheap these days—as cheap as £1 in fact. [Beamer] had purchased one himself, but quickly grew bored with just pointing it at the walls. He decided to figure out if he could use it for some kind of communication, and whipped up a circuit to test it out.
This is a companion discussion topic for the original entry at https://hackaday.com/2024/05/20/trying-to-build-a-communications-device-with-a-1-pound-laser-and-a-7805/