In the case of the GoCuff, it is a holder that fits on the sleeve designed for a smartphone. What science fiction book or film is this from? Why, my own, of course. All right, this is a cheap promotion for The Messengers, Book 1: Worlds Apart, which you can get on Amazon.
In my book, which took place in the future, everyone wore a computer on their forearm. I called it a PWC, or Personal Wrist Computer, and this was before the age of smartphones. The GoCuff is a way to keep a smartphone on your forearm so you can access all the apps.
It is designed for all smartphones, but mostly it is designed for use with Fitness apps, and can track elevation for skiing and snowboards.
The GoCuff is a Kickstarter project, and it made its goals already with some to spare. I would imagine that it will probably hit the market very, very soon. I don’t know what the price will be.