I printed this model with the front part having a concentric pattern and the bottom shell having a hilbert curve pattern. Supports are needed because of the ring. 

I left a gap between the rings because I'm lazy and also the original keyfob has a gap there. I have already used the gap to pop the keyfob apart, so I guess it has some utility. The 3mf file is there if you want to move the ring on the back side up a little.

I found that for some reason, the range on the keyfob is dramatically extended if you use the new TPMS-FK infill! I am using black creality petg.