Slip-On Filament Sensor Alarm

Update: June 7, 2018: Revised models to be less prone to false no-filament alarms.

I couldn't find an out-of-filament alarm that could be attached to filament without threading through the device. I wanted to only put on the alarm when the spool is near empty and might run out and not be bothered with it for full spools. This alarm can be installed while the printer is printing and will sound a loud alarm when the filament runs out.

Hopefully this will provide enough time to manually pa