My requirements for the filament runout sensor enclosure:

1. Easy to print
2. No additional hardware needed
3. Mounted to the printer, not dangling somewhere
4. Wires going out the back to avoid the x-axis
5. Act as a guide so it doesn't put stress on the filament

UPDATE 2021-09-30
I added a lid that just slides on to keep the switch tightly in place. I also made the suggested change to allow for PTFE tubing if desired. I'll keep the old lid-less and PTFE-less version around for posterity. So either use the base and lid models together or use the old model without the lid by itself.

Buy the cheap micro switches microswitches tiny switches from your favorite provider (I got 10 for $8 from Amazon) and this should plop right in. It's really easy to get going if you're using octoprint as the Octoprint-Enclosure plugin does all the heavy lifting for you. There are several other plugins that exist but seem to no longer be maintained or can't run a GCODE command (e.g. M600 for filament change) when the sensor is tripped.

This was a cheap and fairly easy addition to my Ender 3 Pro, but should work for most Creality printers with the same extruder setup. Enjoy!

Tweaked the design by rghawi to meet all my needs. Needed to change the orientation and where the filament comes out so that it hits the extruder without bending at all. https://www.thingiverse.com/thing:4116904

Octoprint-Enclosure Plugin - https://plugins.octoprint.org/plugins/enclosure/