One of the simplest, and compatible Filament Sensor kits.
This little device will help save many a 3D Print from failing from the gamble it is, guessing if you have enough Filament left on a spool for a 3D Print.

Filament Diameter: 1.75mm
Nominal Voltage: 5V
Output Voltage: 24V
Current: 20mA
Size: 26mm x 36mm x 57mm
Weight: 100g