Check these beauties out. Not for sale. I did some googling and see that these are still for sale as data recorders.
These specific devices were used to track slot play at casinos and bars.
First time I've seen or heard about these. How did they work? Predecessor to player's slot cards?
I got these from Phil Jensen. Didn't get a clear idea of how they worked but if you google "ibutton", you get a whole raft of information. And apparently, they are still used because they are still for sale for different applications.
I didn't spend too much time looking, but my initial search didn't reveal any images of machines using these, which is what I was hoping for.