Remember when you used to put your key under a rock in the front yard (maybe you're still doing it, but don't tell us, OK)? Well, soon you may be able to keep your cryptocurrency inside an artificial, oddly shaped rock.

On Wednesday, Block (the company formerly known as Square) hardware chief Jesse Dorogusker tweeted a photo of five rock-like, hexagonal gadgets which are obviously not ordinary rocks. They've got USB ports and what look like fingerprint readers on top, but no visible display of any kind.

The tweet was retweeted by Block CEO Jack Dorsey with the caption "rockey."

Tweet may have been deleted

Mysterious as these posts are, it's not so hard to conclude that this "rockey" thingy is a hardware cryptocurrency wallet Block has been working on for a while. The company says it'll provide users with a mobile app, allowing them to "safely own and manage their bitcoin," as well as a hardware wallet that "adds additional layers of security when moving money and acts as a self-serve recovery kit when a customer loses their mobile wallet."

The gadgets shown in Dorogusker's photo aren't finished products, however. These devices are "some prototypes we are experimenting with for the hardware component of the wallet, which also will include a mobile app and a set of self-serve recovery tools," Lindsey Grossman, head of product, marketing, and partnerships for Block’s wallet told The Verge. There's no word on when these devices might actual hit the market, or how far they are from their final form.

Cryptocurrency hardware wallets are definitely a thing, and they come in many shapes and sizes, with some of the most popular ones coming from Trezor and Ledger. These wallets typically support many cryptocurrencies and come with a display, while Block's prototypes seem to be far simpler and focused on Bitcoin alone.