The ysalamiri cage was found on Zann Consortium Mobile Defense Units. The Consortium used these cages, each of which contained a single ysalamir from Myrkr to make bubbles within the Force, making the areas they contained impossible for users of the Force to access their power. This gave Consortium forces an advantage when encountering Force-sensitive beings.
The only true canonical use of this was during the Theft on Coruscant. During gameplay, ysalamiri cages are only buildable when Myrkr is under Zann Consortium control.
- Star Wars: Empire at War: Forces of Corruption (First appearance)