This is a replacement cover for a Scosche Rhythm+ optical heart rate monitor (https://www.scosche.com/catalog/product/view/id/9140). My cover tore after a couple of years of use. Without a functional cover, water gets in very easily and my device stopped working until I had dried it out. I don't think a 3D printed cover will be waterproof, but it might just be good enough for running in the dry. I printer this out of PETG filament on an Ormerod. The original design was produced using Solvespace (the design files are attached).

RepRap

RepRap Ord Bot Hadron

No

No

0.3mm

25%