Yup, basically just an infrared led and a photoresistor connected to a function generator chip and an echo chip.
It lacks the volume control, but i know now how i could make one, so maybe i’ll upgrade it some day.
Hmm, not sure really, i have played a lot with it though. I know i have used it in at least one track in the past, but it’s a long time ago and i can’t remember wich one. 
Playing with it rather than using it in a composition is also 100% valid, of course. But maybe, if you still have it, dig it out and use it on a new tune? It’s a cool device!
Oh, it’s a theremin, some of my favorite instruments! This really gave me a flashback of the good old days of YouTube when people posting creative gadgets and kinetic sculptures instead of clickbaits like these days.
Nice!
I am having a lot of fun with my Nintendo Switch and pocket operators to make my sampled beats and live loops, with the Korg gadget app and its sound banks. Its a perfect setup for airline travel where desk space comes at a very high premium, and you still wanna look kool making music with stuff that you can put in your pockets with wires hanging out for kicks. Also my cyberdeck on Raspberry Pi running Renoise and Csound firing on all cylinders. But I cannot imagine selling my hardware gear, things like the Kemper, the SP404, MPCs and such, they are all legacy items with history and culture behind it, they will last years and potentially outlast even our own lifetimes. Better to keep them and bequeath them to your next of kin.