While a Switch’s Joy-Cons connect via a Bluetooth signal and probably could’ve worked with the Steam Deck on their own with minimal tinkering, the goal of this mod — nicknamed the “Steamjoy” — was to create a Steam Deck case that Joy-Cons could actually connect to in the same way they connect to the Switch.
Mrblackm123 used a third-party plastic shell as a base, gutted the Steam Deck of its components, and placed them all in their new housing. The new housing features a ventilation fan on the back and a small internal speaker, sourced from a smartphone, to play sounds and music. Most importantly, though, the sides of the case feature rails for the Joy-Cons to slide and snap into, just like a Switch. The functionality of the Steam Deck hasn’t been impacted; it can still run games as it usually would, though mrblackm123 needed to map the Joy-Cons’ plus button to bring up the digital keyboard for desktop mode since there was no longer a dedicated button to call it up.
Mrblackm123 is planning to continue refining their creation, with the next major goal being a proper hard connection between the Joy-Cons and the case. At the moment, though the Joy-Cons are slid in, they’re only connected to the case via Bluetooth; the case doesn’t have connector pins like a real Switch, so the Joy-Cons can’t interface directly with it or charge from it.