I love the utility of Square (and Paypal, etc...) for mobile payments. Being able to take credit & debit cards from my smartphone really helps me when I'm doing on-site work for a client, or meeting up with someone to give them a consult, and I don't think I've written a check now in over two years.
But you know what isn't a lot of fun? digging around for my reader in the bottom of my bag or a pocket, or worse, forgetting it and leaving it at home or in another pair of trousers.
To help me keep tabs on mine, and to ensure that I've always got it on hand, I just drew up this keychain carrier. It's got a detent rib to help snuggly hold the reader by engaging the card-reader slot, and a top-lid that has a post to engage the body of the case to help it stay aligned and on when on a key-ring. Because the post is a through-hole, you can easily push it off from the back-side.